docs/library/index: Add hint about using help('modules') for discovery.
@@ -40,6 +40,11 @@ best place to find general information of the availability/non-availability
of a particular feature is the "General Information" section which contains
information pertaining to a specific `MicroPython port`.
+On some ports you are able to discover the available, built-in libraries that
+can be imported by entering the following at the REPL::
+
+ help('modules')
+
Beyond the built-in libraries described in this documentation, many more
modules from the Python standard library, as well as further MicroPython
extensions to it, can be found in `micropython-lib`.
