Add github templates for issue reports and new pull requests

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,14 @@
+Hey! Thanks for you contribution. To help you with that pull request,
+we have here some useful informations for you.
+
+Did you know:
+  - Our development happens on `next` branch. So should yours. Please
+    ensure your base is `next`. More information [here](https://github.com/bhilburn/powerlevel9k/wiki/Developer's-Guide).
+  - We have a lot of unit tests (in `test` dir). It would be awesome,
+    if you would add one for your feature.
+  - For manual tests there are Vagrant files and Docker files prepared.
+    Just have a look at the [test readme](https://github.com/bhilburn/powerlevel9k/blob/next/TESTS.md)
+  - Our [wiki](https://github.com/bhilburn/powerlevel9k/wiki) is quite
+    packed with loads of information about how to configure this theme.
+    If your feature has some flexpoint, the configuration help should
+    probably go there or in the README.