Add CONTRIBUTING.md and GitHub templates

.github/ISSUE_TEMPLATE.md

@@ -0,0 +1,24 @@
+### Problem Description
+
+Describe the problem you are having, what you expect to happen
+instead, and how to reproduce the problem.
+
+### Configuration File
+
+Please include the smallest configuration file that reproduces the
+problem you are experiencing:
+
+```haskell
+module Main (main) where
+
+import XMonad
+
+main :: IO ()
+main = xmonad def
+```
+
+### Checklist
+
+  - [ ] I've read [CONTRIBUTING.md](https://github.com/xmonad/xmonad/blob/master/CONTRIBUTING.md)
+
+  - [ ] I tested my configuration with [xmonad-testing](https://github.com/xmonad/xmonad-testing)

.github/PULL_REQUEST_TEMPLATE.md

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+### Description
+
+Include a description for your changes, including the motivation
+behind them.
+
+### Checklist
+
+  - [ ] I've read [CONTRIBUTING.md](https://github.com/xmonad/xmonad/blob/master/CONTRIBUTING.md)
+
+  - [ ] I've confirmed these changes don't belong in xmonad-contrib instead
+
+  - [ ] I tested my changes with [xmonad-testing](https://github.com/xmonad/xmonad-testing)
+
+  - [ ] I updated the `CHANGES.md` file