Make it clear that a pull request should only have ONE update or feat…

…ure.

CONTRIBUTING.md

@@ -9,6 +9,7 @@ In order for your code to make it in, several conditions must be met:
   to code.
 * Please talk to the maintainers (@madrobby and @mislav) first if you want
   to write a plugin, those are better kept in their own repositories.
+* Fix only ONE thing or have only ONE feature in your pull request. If you have multiple unrelated code updatates, please submit a seperate pull request for each one.
 * **Your pull request must be written in English and be accompanied by a
   detailed description**, ideally something we can use as documentation.
   If you're not fluent in English, try your best and let us know so we'll help!