Grouping CONTRIBUTING into digestable sections

The current document is very much a wall of text. This commit begins to re-structure that information into logical groups.

CONTRIBUTING.md

@@ -1,8 +1,17 @@
-A good way to help is to test, and report bugs.
-See http://www.chiark.greenend.org.uk/~sgtatham/bugs.html if you
-want to help that way. Testing is invaluable in making a piece
+# Contributing to Monero
+
+A good way to help is to test, and report bugs. See
+[How to Report Bugs Effectively (by Simon Tatham)](http://www.chiark.greenend.org.uk/~sgtatham/bugs.html)
+if you want to help that way. Testing is invaluable in making a piece
 of software solid and usable.
 
+
+## General Guidelines
+
+* Comments are encouraged.
+* If modifying code for which Doxygen headers exist, that header must be modified to match.
+* Tests would be nice to have if you're adding functionality.
+
 Patches are preferably to be sent via a github pull request. If that
 can't be done, patches in "git format-patch" format can be sent
 (eg, posted to fpaste.org with a long enough timeout and a link
@@ -16,15 +25,12 @@ modifying is encourgaged. Proper squashing should be done (eg, if
 you're making a buggy patch, then a later patch to fix the bug,
 both patches should be merged).
 
+## Commits and Pull Requests
+
 Commit messages should be sensible. That means a subject line that
 describes the patch, with an optional longer body that gives details,
 documentation, etc.
 
-Comments are encouraged.
-
-If modifying code for which Doxygen headers exist, that header must
-be modified to match.
-
 When submitting a pull request on github, make sure your branch is
 rebased. No merge commits nor stray commits from other people in
 your submitted branch, please. You may be asked to rebase if there
@@ -32,5 +38,3 @@ are conflicts (even trivially resolvable ones).
 
 PGP signing commits is strongly encouraged. That should explain why
 the previous paragraph is here.
-
-Tests would be nice to have if you're adding functionality.