Style changes on CONTRIBUTORS

CONTRIBUTING.md

@@ -0,0 +1,13 @@
+# Contributing
+
+### Add an entry to the changelog
+
+Please don't forget to update [CHANGELOG.md](CHANGELOG.md) and describe your changes (in the "unreleased" section), this makes the release of a new `bat` version much easier.
+
+Each entry should follow the following format:
+```
+- Short description of what has been changed, see #123 (@user)
+```
+
+Where `#123` is your PR's number or ticket and `@user` is you Github's username. 
+