Documentation nits

[Wolfgang Laun]

Concerning https://www.gnu.org/software/gawk/manual/gawk.html, valid for
5.3.
(a) Section 4.7.1, 1st paragraph, 1st line:
s/contains/contain/
(b) I suggest that this
   s/double quote/quotation mark/g
should be applied to the entire document because this is the official name
of U+0022. It will improve, in particular, Section 4.5.4, Working With
Comma Separated Value Files, where the duplication of double quotes is
discussed.
(c) Regarding 4.7 and the initial note I think that the section need not be
rewritten; however, it might be extended with suitable notes that (1) it
does not apply at all if --csv is used, (2) would apply if a non-standard
variant of CSV needs to be implemented, (3 - optional) it addresses legacy
code, prior to version 5.3.

Regards
Wolfgang