Update documentation of the ForceReply class

[schvv31n]

Checklist for PRs

• Added .. versionadded:: version, .. versionchanged:: version or .. deprecated:: version to the docstrings for user facing changes (for methods/class descriptions, arguments and attributes)
• Created new or adapted existing unit tests
• Added myself alphabetically to AUTHORS.rst (optional)

[Bibo-Joshi]

Hi. Thanks for the PR! However, this note is a bit overly specific IMHO. the official Telegram docs already state that only messages without reply markup or with an inline keyboard can be edited.

One can surely argue that this note should be repeated in PTBs docs somewhere and I've added it to #2633 (see #2633 (comment)). If you're interested, you're very welcome to tackle this in a new PR :)