Aim: unified POD, user more satisfied, script better structured

The plurals in -function and -nosymbol are corrected to singulars.
That's how the script works now. I think this describes the syntax better.
The plurar suggests multiple FILE arguments might be possible. So this
seems more coherent.

Other notes:
- paragraphing correction
- article correction

Signed-off-by: Tomasz Warniełło <tomasz.warniello@gmail.com>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Disliked-by: Akira Yokosawa <akiyks@gmail.com>
Link: https://lore.kernel.org/r/20220218181628.1411551-7-tomasz.warniello@gmail.com


Signed-off-by: Jonathan Corbet <corbet@lwn.net>