cherry-pick/revert: error-help message rewording.

It said "after fixing up, commit the result using -F .msg", but
it was not clear for new people how "fix up" should be done.
Hint "git-update-index <path>".

We could recommend "git commit -a -F .msg" instead, but I am
hesitant to give that suggestion in the blind -- you could do a
cherry-pick, revert or a merge in general in a dirty working
tree as long as local modifications do not overlap with the
merge, but using "commit -a" would include them in the result.

Signed-off-by: Junio C Hamano <junkio@cox.net>

git-revert.sh

@@ -141,8 +141,9 @@ git-read-tree -m -u $base $head $next &&
 result=$(git-write-tree 2>/dev/null) || {
     echo >&2 "Simple $me fails; trying Automatic $me."
     git-merge-index -o git-merge-one-file -a || {
-	    echo >&2 "Automatic $me failed.  After fixing it up,"
-	    echo >&2 "you can use \"git commit -F .msg\""
+	    echo >&2 "Automatic $me failed.  After resolving the conflicts,"
+	    echo >&2 "mark the corrected paths with 'git-update-index <paths>'"
+	    echo >&2 "and commit with 'git commit -F .msg'"
 	    case "$me" in
 	    cherry-pick)
 		echo >&2 "You may choose to use the following when making"