rev-list --remove-empty: add minimum help and doc entry.

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

Documentation/git-rev-list.txt

@@ -14,6 +14,7 @@ SYNOPSIS
 	     [ \--min-age=timestamp ]
 	     [ \--sparse ]
 	     [ \--no-merges ]
+	     [ \--remove-empty ]
 	     [ \--all ]
 	     [ [ \--merge-order [ \--show-breaks ] ] | [ \--topo-order ] ]
 	     [ \--parents ]
@@ -80,6 +81,9 @@ OPTIONS
 	(still subject to count and age limitation), but apply
 	merge simplification nevertheless.
 
+--remove-empty::
+	Stop when a given path disappears from the tree.
+
 --all::
 	Pretend as if all the refs in `$GIT_DIR/refs/` are
 	listed on the command line as <commit>.

rev-list.c

@@ -21,6 +21,7 @@ static const char rev_list_usage[] =
 "    --min-age=epoch\n"
 "    --sparse\n"
 "    --no-merges\n"
+"    --remove-empty\n"
 "    --all\n"
 "  ordering output:\n"
 "    --merge-order [ --show-breaks ]\n"