Rephrasing contribution guide; removing CompCert due to notable non-freedom

CONTRIBUTING.md

@@ -5,19 +5,28 @@ alone, and I welcome pull requests. To make sure that we're all on the same
 page, here are some guidelines to follow for submitting pull requests for this
 list.
 
-## Ensure that everything you link to is free (as in freedom) ##
+## What would be great ##
+
+Obviously, it's your choice what you want to contribute - or not
+contribute. However, if you're looking for something that would help awesome-c,
+check the current issues, especially those tagged with 'help wanted'. Pull
+requests addressing these are particularly great!
+
+## How to contribute ##
+
+Now for the mechanics of the process, and some do's and don't's.
+
+### Ensure that everything you link to is free (as in freedom) ###
 
 This is highly important - this list *only* contains freedom-respecting things!
 If you are sending a pull request linking to code, ensure it is licensed under a
-[freedom-respecting license][1]; if you are linking to assets of any kind, make
-sure that [they are the same][2]. For games, be especially careful that they are
-both.
+[freedom-respecting license][1].
 
-## Indicate the license for anything you add clearly ##
+### Indicate the license for anything you add clearly ###
 
-Ensure that you use the correct name for the license (as per [this][1]
-or [this][2]), and indicate any further restrictions clearly. Also check if the
-license is in use already - if it is, don't create another link to it.
+Ensure that you use the correct name for the license (as per [this][1]), and
+indicate any further restrictions clearly. Also check if the license is in use
+already - if it is, don't create another link to it.
 
 ## Maintain alphabetical order within sections ##