Update the main README to explain how to contribute to Documentation tasks

Author: imath

README.md

@@ -1,2 +1,15 @@
-# bp-documentation
-Tasks tracker for the BuddyPress documentation resources
+# BP Documentation tasks tracker
+
+This repository is used by the BuddyPress team to track required Documentation tasks in order to organize collaboration about these.
+
+## BP Codex migration meta task
+
+You can first contribute to updating BP Documentation resources by picking [one of these listed BP Codex pages](./data/README.md) and submitting a new Issue (Migrate or Ignore task) to this repository.
+
+## BP Documentation meta task
+
+You can also contribute to adding BP Documentation resources by submitting a new Issue (Add task) to this repository.
+
+## BP Documentation maintenance meta task
+
+Once we'll have a strong candidate to "release" for each available handbook we're working on from the buddypress GitHub repository, we'll add a new site about it into the BuddyPress.org network and we'll see what's the best option to keep it updated (Synchronizing GitHub or using the WordPress site's workflow).