Update README

README.md

@@ -12,4 +12,37 @@ operations.
 Commands
 --------
 
-repmgr cluster event [--all] [--node-id] [--node-name] [--event] [--event-matching]
+Currently available:
+
+    repmgr master register
+    repmgr master unregister
+
+    repmgr standby clone
+    repmgr standby register
+    repmgr standby unregister
+    repmgr standby promote
+    repmgr standby follow
+
+    repmgr cluster event [--all] [--node-id] [--node-name] [--event] [--event-matching]
+
+
+Backwards compatibility
+-----------------------
+
+`repmgr` is now implemented as a PostgreSQL extension.
+
+Metadata tables have been revised and are not backwards-compatible
+with 3.x. (however future DDL updates will be easier as they can be
+carried out via the ALTER EXTENSION mechanism.
+
+TODO: extension upgrade script for pre-4.0
+
+Some configuration items have had their names changed for consistency
+and clarity e.g. `node` => `node_id`. `repmgr` will issue a warning
+about deprecated/altered options.
+
+Some configuration items have been changed to command line options,
+and vice-versa, e.g. to avoid hard-coding things like a node's
+upstream ID which might change.
+
+TODO: possibly add a config file conversion script/function.