Contributing: improve the text

As GH was so kind as to point me to the "contributing guidelines which have been changed since you last contributed" I quickly scanned through the file and most notably, came across a link to the WPCS wiki page, while this link should have gone to the VIPCS wiki.

As I was editing the file now anyway, I've made some other changes along the way.

* Ask people to search the issue list before opening an issue.
* Made a little table to make it easier for people to report upstream issues to the correct repository.
* Updated the "custom properties" link to point to the VIPCS wiki.
* Updated the PHPUnit installation link.
* Updated the `phpunit.xml` example to be in line with the current `phpunit.xml.dist` file.
* Updated the expected unit test output.

.github/CONTRIBUTING.md

@@ -7,11 +7,25 @@ Hi, thank you for your interest in contributing to the VIP Coding Standards! We
 Before reporting a bug, you should check what sniff an error is coming from.
 Running `phpcs` with the `-s` flag will show the name of the sniff with each error.
 
+Please search the repository before opening an issue to verify that the issue hasn't been reported already.
+
 Bug reports containing a minimal code sample which can be used to reproduce the issue are highly appreciated as those are most easily actionable.
 
 ### Upstream Issues
 
-Since VIPCS employs many sniffs that are part of PHPCS, and makes use of WordPress Coding Standards sniffs, sometimes an issue will be caused by a bug upstream and not in VIPCS itself. If the error message in question doesn't come from a sniff whose name starts with `WordPressVIPMinimum`, the issue is probably a bug in PHPCS itself, and should be [reported there](https://github.com/squizlabs/PHP_CodeSniffer/issues).
+Since VIPCS employs many sniffs that are part of PHPCS, and makes use of WordPress Coding Standards sniffs, sometimes an issue will be caused by a bug upstream and not in VIPCS itself. If the error message in question doesn't come from a sniff whose name starts with `WordPressVIPMinimum`, the issue is probably an upstream bug.
+
+To determine where best to report the bug, use the first part of the sniff name:
+
+Sniffname starts with | Report to
+--- | ---
+`Generic` | [PHP_CodeSniffer](https://github.com/squizlabs/PHP_CodeSniffer/issues/)
+`PSR2` | [PHP_CodeSniffer](https://github.com/squizlabs/PHP_CodeSniffer/issues/)
+`Squiz` | [PHP_CodeSniffer](https://github.com/squizlabs/PHP_CodeSniffer/issues/)
+`VariableAnalysis` | [VariableAnalysis](https://github.com/sirbrillig/phpcs-variable-analysis/issues/)
+`WordPress` | [WordPressCS](https://github.com/WordPress/WordPress-Coding-Standards/issues/)
+`WordPressVIPMinimum` | [VIPCS](https://github.com/Automattic/VIP-Coding-Standards/issues/) (this repo)
+`Generic`, `PSR2` or `Squiz` | [PHP_CodeSniffer](https://github.com/squizlabs/PHP_CodeSniffer/issues/)
 
 ----
 
@@ -42,7 +56,7 @@ The sniffs and test files - not test _case_ files! - for VIPCS should be written
 When writing sniffs, always remember that any `public` sniff property can be overruled via a custom ruleset by the end-user.
 Only make a property `public` if that is the intended behaviour.
 
-When you introduce new `public` sniff properties, or your sniff extends a class from which you inherit a `public` property, please don't forget to update the [public properties wiki page](https://github.com/WordPress-Coding-Standards/WordPress-Coding-Standards/wiki/Customizable-sniff-properties) with the relevant details once your PR has been merged into the `develop` branch.
+When you introduce new `public` sniff properties, or your sniff extends a class from which you inherit a `public` property, please don't forget to update the [public properties wiki page](https://github.com/Automattic/VIP-Coding-Standards/wiki/Custom-properties-for-VIPCS-Sniffs) with the relevant details once your PR has been merged into the `develop` branch.
 
 ## Unit Testing
 
@@ -61,7 +75,7 @@ N.B.: If you installed VIPCS using Composer, make sure you used `--prefer-source
 If you already have PHPUnit installed on your system: Congrats, you're all set.
 
 If not, you can navigate to the directory where the `PHP_CodeSniffer` repo is checked out and do `composer install` to install the `dev` dependencies.
-Alternatively, you can [install PHPUnit](https://phpunit.de/manual/5.7/en/installation.html) as a PHAR file.
+Alternatively, you can [install PHPUnit](https://phpunit.readthedocs.io/en/7.5/installation.html) as a PHAR file.
 
 ### Before running the unit tests
 
@@ -71,11 +85,13 @@ For the unit tests to work, you need to make sure PHPUnit can find your `PHP_Cod
 
 The easiest way to do this is to add a `phpunit.xml` file to the root of your VIPCS installation and set a `PHPCS_DIR` environment variable from within this file. Make sure to adjust the path to reflect your local setup.
 ```xml
-<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-	xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/6.3/phpunit.xsd"
-	beStrictAboutTestsThatDoNotTestAnything="false"
-	bootstrap="./tests/bootstrap.php"
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/7.2/phpunit.xsd"
 	backupGlobals="true"
+	bootstrap="./tests/bootstrap.php"
+	beStrictAboutTestsThatDoNotTestAnything="false"
 	colors="true">
 	<php>
 		<env name="PHPCS_DIR" value="/path/to/PHP_CodeSniffer/"/>
@@ -86,7 +102,7 @@ The easiest way to do this is to add a `phpunit.xml` file to the root of your VI
 ### Running the unit tests
 
 * Make sure you have registered the directory in which you installed VIPCS with PHPCS using;
-    
+
     ```sh
     phpcs --config-set installed_paths path/to/VIPCS
     ```
@@ -99,13 +115,13 @@ The easiest way to do this is to add a `phpunit.xml` file to the root of your VI
 
 Expected output:
 ```
-PHPUnit 7.5.12 by Sebastian Bergmann and contributors.
+PHPUnit 7.5.20 by Sebastian Bergmann and contributors.
 
-...........................................                       43 / 43 (100%)
+..........................................                        42 / 42 (100%)
 
-44 sniff test files generated 119 unique error codes; 0 were fixable (0%)
+43 sniff test files generated 117 unique error codes; 0 were fixable (0%)
 
-Time: 380 ms, Memory: 30.00MB
+Time: 246 ms, Memory: 32.00 MB
 ```
 
 ### Unit Testing conventions