[IMPR] Add corresponding API page links to APISite method docstrings
[IMPR] Add corresponding API page links to APISite method docstrings

Modify the docstring of APISite methods in login .py.

Bug: T100521
Change-Id: I0a7de965f3ee446791067520251f784c2d5f79b6

wikimedia/pywikibot-core,PersianWikipedia/pywikibot-core,wikimedia/pywikibot-core