Notice that IANA currently uses the "media types" term:

[RFC2046] specifies that Media Types (formerly known as MIME types) and Media
Subtypes will be assigned and listed by the IANA.

Just an idea, feel free to ignore it: sometimes the following approach may be used to estimate --help message. Try to read man page generated by help2man. Perhaps epilog may be added to ArgumentParser constructor, however I am unsure concerning recommendations within the Python project.