doc improvement for dotglob

[Ian Kelling]

The docs currently say:

"When a pattern is used for filename expansion, the character '.' at
the start of a filename or immediately following a slash must be matched
explicitly, unless the shell option 'dotglob' is set. 

The last bit should be changed to say

unless the shell option 'dotglob' is set and the file is not named '.'
or '..'. 

And dotglob's dedicated section has similar wording to change.

I looked at making a patch, but it seems the docs are repeated in
many formats, so I figured I'd just post this first.

--
Ian Kelling
https://iankelling.org