GitHub: Introduce Issue Guidelines

Taken from Android-Nify.

This is helpful when somebody wants to report an issue.

.github/CONTRIBUTING.md

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+## Issue guidelines
+
+Hey there! You found a problem with the module and found your way here to report it? Great! But there are some things you have to keep in mind before submitting a new issue:
+
+* **Check for duplicates**. Use the search function to search for keywords matching your issue. If there already is one which sounds similar to your one, please reply there instead of opening a new issue. Only exception are SystemUI crashes as they can be caused by various reasons. If any contributor finds a duplicate (or the same crash) he will close it.
+
+* **Always attach your Xposed log**. For the false positives, please enable debug logging and attach them. If an app crashes though you'll have to add a logcat. Use Google to learn how to capture a logcat.
+
+Note that there is no time limit in which the issue will be adressed. Some get fixed quickly, others take some time. Don't open a new issue because you think we forgot about the old one - we don't "forget" issues.

.github/ISSUE_TEMPLATE.md

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+<!--
+Hey there! You found a problem with the module and found your way here to report it? Great! But there are some things you have to keep in mind before submitting a new issue:
+
+First, CHECK FOR DUPLICATES. Use the search function to search for keywords matching your issue. If there already is one which sounds similar to your one, please reply there instead of opening a new issue. Only exception are SystemUI crashes as they can be caused by various reasons. If any contributor finds a duplicate (or the same crash) he will close it.
+
+Second, ALWAYS ATTACH YOUR XPOSED LOG. If an app crashes though you'll have to add a logcat. Use Google to learn how to capture a logcat.
+
+If the issue is new, go ahead and DESCRIBE YOUR ISSUE AS PRECISE AS POSSIBLE, add screenshots or videos if necessary.
+
+Note that there is no time limit in which the issue will be adressed. Some get fixed quickly, others take some time. Don't open a new issue because you think we forgot about the old one - we don't "forget" issues.
+
+Now that you've read all of this (and hopefully followed the instructions) you can add the description and logs. Do with this text what you want, it won't appear in the issue anyways.
+-->
+
+**Description**
+
+**Xposed log / logcat**