DOC: add contributors to 1.3 release notes
I think we should do this for the rc.

We will be publishing the docs at https://pandas.pydata.org/pandas-docs/version/1.3.0/ and linked from the rc announcement. (It's the same url for the actual release and the rc docs are replaced)

we haven't yet released 1.2.5 so the 1.2.5 tag does not yet exist. used 1.2.4 for now.
don't you need the tag to exist for this to work? (1.3) > don't you need the tag to exist for this to work? (1.3)

it should be `.. contributors:: v1.2.5..v1.3.0|HEAD` for the actual release, but the v1.2.5 tag does not yet exist.

maybe it could be ``.. contributors:: v1.2.5|v1.2.4..v1.3.0|HEAD`` or we could merge this and update before the actual 1.3 release