Add some info to contributing.md

Blatantly copied from the Swarm repository, but
at least there's some info now in the document
that GitHub will link to when opening issues and PR's

Signed-off-by: Sebastiaan van Stijn <[email protected]>

Author: thaJeztah

CONTRIBUTING.md

@@ -1,3 +1,16 @@
 # Contributing to libcompose
 
-You should do that...
+Want to hack on Libcompose? Awesome! Here are instructions to get you
+started.
+
+Libcompose is part of the [Docker](https://www.docker.com) project, and
+follows the same rules and principles. If you're already familiar with
+the way Docker does things, you'll feel right at home.
+
+Otherwise, go read Docker's
+[contributions guidelines](https://github.com/docker/docker/blob/master/CONTRIBUTING.md),
+[issue triaging](https://github.com/docker/docker/blob/master/project/ISSUE-TRIAGE.md),
+[review process](https://github.com/docker/docker/blob/master/project/REVIEWING.md) and
+[branches and tags](https://github.com/docker/docker/blob/master/project/BRANCHES-AND-TAGS.md).
+
+Happy hacking!