magit-tag-{*}: improve git usage info in doc-strings
magit-reset-{*}: improve git usage info in doc-string

and other cosmetic adjustments.
magit-stash-{*}: improve git usage info in doc-string
Merge branch 'n/git-usage-doc-string' into next
magit-popup.el: add "Settings" top-level section

Turn "Custom Options", "Custom Faces", "Keymaps", and "Buttons"
into subsections.  The "Custom " prefix of the first two is new.

And yes, users may modify the buttons to customize their
appearance, using `button-type-put'.  By turning "Buttons"
in a subsection of "Settings" we hint at that.
magit-popup{,-faces}: new custom groups

The existing `magit-popups' group and the new `magit-popup' group serve
different purposes.  But because that might not be immediately obvious,
add cross-references.