It's a bit of a pitfall with user C modules that including them in the
build does not automatically enable them. This commit changes the docs and
examples for user C modules to encourage writers of user C modules to
enable them unconditionally. This makes things simpler and covers most use
cases.
See discussion in issue #6960, and also #7086.
Signed-off-by: Damien George <damien@micropython.org>