Fix TF start docstrings
(This is not an urgent fix and can wait until after the release)

Our TF models include a cookie-cutter docstring explaining how inputs can be passed, which is very prominent in the online docs. Parts of this are old and confusing, and it had a few errors, both grammar and variable names. I rewrote it, which should hopefully reduce user confusion in future!
_The documentation is not available anymore as the PR was closed or merged._