Provide a more meaningful initial "From " line when using --compose in git-send-email.

git-send-email, when used with --compose, provided the user with a mbox-format
file to edit.  Some users, however, were confused by the leading, blank, "From
" line, so this change puts the value that will appear on the From: line of the
actual email on this line, along with a note that the line is ignored.

Signed-off-by: Ryan Anderson <ryan@michonline.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>

git-send-email.perl

@@ -125,7 +125,7 @@ if ($compose) {
 	# effort to have it be unique
 	open(C,">",$compose_filename)
 		or die "Failed to open for writing $compose_filename: $!";
-	print C "From \n";
+	print C "From $from # This line is ignored.\n";
 	printf C "Subject: %s\n\n", $initial_subject;
 	printf C <<EOT;
 GIT: Please enter your email below.