Doc glitch about -f and is_file

[jimav]

Current docs say

Note: "is_file" is not "-f" because "-f" is not the opposite of "-d".
"-f" means "plain file", excluding symlinks, devices, etc. that often
can be read just like files.

This isn't quite correct because -f symlink_to_file returns true.

Suggest changing the wording to:

"-f" means a plain file (or a symlink to a plain file), but not devices, etc. that often
can be read just like files.

[ap]

Seems to me that symlinks are sort of irrelevant and should just be left out of the text. Something like

C<-f> means "plain file", excluding filesystem objects like devices
and sockets that often can be read just like files.