fortune/freebsd-tips: Fix markup and wording

'ps' is not a word - rather, it is a utility with its own manual page.
As every other utility referenced in the file has it, append the
relevant manual section that ps(1) can be found in.

While here, also wordsmith a sentence to avoid awkward phrasing, and fix
a typo.

Pointy hat to: me
Reported by: danfe, brueffer, maxim