CONTRIBUTING.md: request :version and :JediDebugInfo output

Also add sections, and fix style instructions.

[ci skip]

CONTRIBUTING.md

@@ -1,9 +1,12 @@
-We <3 pull requests!
+# We <3 pull requests!
 
  1. Fork the Repo on github.
  2. Add yourself to AUTHORS.txt
  3. Add a test if possible.
  4. Push to your fork and submit a pull request.
 
-Please use PEP8 as a Python code style. For VIM, just stick try to style your
-code similar to the jedi-vim code that's there.
+Please use PEP8 as a Python code style. For VIM, just try to style your
+code similar to the jedi-vim code that is already there.
+
+# Bug reports
+Please include the output of `:version` and `:JediDebugInfo`.