man: reword tmpfiles.d descriptions to refer less to previous descriptions

man: reword tmpfiles.d descriptions to refer less to previous descriptions

I think it is OK if some option is described as "similar to ..., but in
addition ...", as long as the "in addition" part is strictly additive this is
unambiguous. Otherwise, we'd have to repeat a lot of text, and then we'd
probably forget to adjust some of the descriptions when doing changes.

But when the "in addition" part is about replacing or removing parts of
functionality, it is better to avoid this pattern and describe the later option
from scratch.

Some paragraph breaks are added and minor changes made. UID/GID is changed to
user/group, since we generally expect user/group names to be used, not numeric
ids.

Fixes #11115.