Update using.rst to advertise full mhu support for GHCi
finally closes #20889 (closed) and in particular addresses #20889 (comment 624435)
Due to a large amount of spam we do not allow new users to create repositories, they are "external" users. If you are a new user and want to create a repository, for example for forking GHC, open a new issue on ghc/ghc using the "get-verified" issue template
finally closes #20889 (closed) and in particular addresses #20889 (comment 624435)