update contributing guidelines layout

docs/CONTRIBUTING.md

@@ -1,8 +1,10 @@
-# General
+# Contributing to Level 13
+
+## General
 
 Level 13 is a personal side project. Bug reports and suggestions are very welcome, but updates happen sporadically and it might take a while for your contributions to be reviewed.
 
-# Issues
+## Issues
 
 You can use issues to submit bug reports or to suggest new features or enhancements to existing features.
 
@@ -11,6 +13,6 @@ You can use issues to submit bug reports or to suggest new features or enhanceme
 * For bugs, write down what happened and what you expected to happen
 * Mention the version number you were playing (you can find it in the bottom left of the page)
 
-# Pull requests
+## Pull requests
 
 If you want to contribute a small bug-fix then by all means do so. Please refrain from sending pull requests containing bigger refactoring or new behaviour.