doc: fix texinfo for short options taking a parameter
* doc/coreutils.texi: (tail invocation): Add missing -s,
along with the existing --sleep-interval description.
(csplit invocation): s/--suffix/--suffix-format/.
(head invocation): Use same variable (COUNT) for -n and --head-count.
(seq invocation): Add opindex items for all options.
(ptx invocation): Likewise.
Fix typo s/--flac-truncation/--flag-truncation/.
(touch invocation): State explicitly that -d takes a parameter,
which also indicates that an '=' is not to be used
for the short option syntax.
(ls invocation): Likewise for the -w option.
Fixes http://bugs.gnu.org/21809