Documentation regarding use of templates is out of date

[plwalsh]

https://nbconvert.readthedocs.io/en/latest/customizing.html specifically needs to reference the difference in the two field names if someone has a cycle to help improve that.

Let me point out another place in the docs that needs to be updated.

As of ver. 7.0.0.rc3, https://nbconvert.readthedocs.io/en/latest/usage.html#convert-latex is wrong: the old option (--template report) instead of the new one (--template-file report) is documented.

Originally posted by @miccoli in #1671 (comment)