DOC: move release note for #36175 (pt1)
xref https://github.com/pandas-dev/pandas/pull/36363/files#r488227748
@simonjayhawkins future note: you could also do it in a single PR (targetting master), and update the diff (to remove the changed in the 1.2 file) when doing the backport. 
(I personally think that is cleaner/clearer, although then meeseekdev won't be able to automate the backport of course ..)