Add an issue template for Github

.github/issue_template.md

@@ -0,0 +1,24 @@
+[We wrote some guidelines to help you
+craft the best Issue / Pull Request possible](https://github.com/moonmoon/moonmoon/CONTRIBUTING.md),
+don't hesitate to take a look at it :-)
+
+---
+
+### Expected behavior
+
+What are you expecting to happen?
+
+### Actual behavior
+
+What happens instead?
+
+### Steps to reproduce
+
+* ... 
+* ...
+* ...
+
+### Moonmoon version
+
+Which version of moonmoon are you using? If you don't know which one is installed,
+try open the file `VERSION` at the root of moonmoon's folder.