help: revise explanation about capability check while selecting merge tool
This is follow up of
7c6044634957 and
cded904f7acc.
This patch adds explanations about:
- notation in capability columns in the table
- how capabilities of external merge tools are treated
#require clang-format test-repo
$ . "$TESTDIR/helpers-testrepo.sh"
$ cd "$TESTDIR"/..
$ for f in `testrepohg files 'set:(**.c or **.cc or **.h) and not "listfile:contrib/clang-format-ignorelist"'` ; do
> clang-format --style file $f > $f.formatted
> cmp $f $f.formatted || diff -u $f $f.formatted
> rm $f.formatted
> done