README: updates for WordPressCS 3.0.0

This commit updates the README guide to be in line with WordPressCS 3.0.0.

This commit:
* Removes the "Last commit to stable" and "Nr of contributors" badges.
* Updates the "Tested on PHP..." badges.
* Updates the table of contents to match the new content of the file.
* Removes the "Project history" section (has been moved to the wiki).
* Makes the pre-requisites for the package more explicit and puts them in a separate section.
* Updates the installation instructions and adds update instructions.
    - Removes the instructions related to stand-alone installs and using `composer create-project`.
    - The new installation instructions take the changes in Composer 2.2 (permission required for plugins to run) into account.
    - The new installation instructions include a link to the end user/ruleset maintainer upgrade guide for WPCS 3.0.0 as the initial upgrade may need extra work.
* Updates references to the Composer PHPCS plugin to make sure these reference the new name and link to the correct GH repo (as the repo has moved).
* Removes the reference to the VIP ruleset which was removed in WPCS 2.0.0 from the "Rulesets" section.
* Adds links to the "customizable properties" section for where to find customizable properties for PHPCS native sniffs and sniffs from PHPCSExtra.
* Adds the `VariableAnalysis` standard and the `VIP Coding Standards` to the list of optional additional rulesets to use.
* Updates the command and output for the example run.
* Removes the links to IDE related tutorials in favour of a link to the wiki (to save us having to maintain this list in multiple places).
* Ensures the text consistently uses `WordPressCS` instead of `WPCS`.

Closes #481
Closes #1821
Closes #1901