scalar: add to 'git help -a' command list

Add 'scalar' as a 'mainporcelain' command in the Git command list. Update
the regex in 'cmd-list.perl' used to match the first line of command
documentation to find 'scalar(1)'.

Helped-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Victoria Dye <vdye@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/cmd-list.perl

@@ -10,7 +10,7 @@ sub format_one {
 	$state = 0;
 	open I, '<', "$name.txt" or die "No such file $name.txt";
 	while (<I>) {
-		if (/^git[a-z0-9-]*\(([0-9])\)$/) {
+		if (/^(git|scalar)[a-z0-9-]*\(([0-9])\)$/) {
 			$mansection = $1;
 			next;
 		}

command-list.txt

@@ -235,3 +235,4 @@ gittutorial                             guide
 gittutorial-2                           guide
 gitweb                                  ancillaryinterrogators
 gitworkflows                            guide
+scalar                                  mainporcelain