add documentation for update-index --unresolve

Signed-off-by: Matthias Kestenholz <matthias@spinlock.ch>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/git-update-index.txt

@@ -15,7 +15,7 @@ SYNOPSIS
 	     [--cacheinfo <mode> <object> <file>]\*
 	     [--chmod=(+|-)x]
 	     [--assume-unchanged | --no-assume-unchanged]
-	     [--really-refresh]
+	     [--really-refresh] [--unresolve]
 	     [--info-only] [--index-info]
 	     [-z] [--stdin]
 	     [--verbose]
@@ -80,6 +80,10 @@ OPTIONS
 	filesystem that has very slow lstat(2) system call
 	(e.g. cifs).
 
+--unresolve::
+	Restores the 'unmerged' or 'needs updating' state of a
+	file during a merge if it was cleared by accident.
+
 --info-only::
 	Do not create objects in the object database for all
 	<file> arguments that follow this flag; just insert

update-index.c

@@ -473,7 +473,7 @@ static void read_index_info(int line_termination)
 }
 
 static const char update_index_usage[] =
-"git-update-index [-q] [--add] [--replace] [--remove] [--unmerged] [--refresh] [--cacheinfo] [--chmod=(+|-)x] [--info-only] [--force-remove] [--stdin] [--index-info] [--ignore-missing] [-z] [--verbose] [--] <file>...";
+"git-update-index [-q] [--add] [--replace] [--remove] [--unmerged] [--refresh] [--really-refresh] [--cacheinfo] [--chmod=(+|-)x] [--assume-unchanged] [--info-only] [--force-remove] [--stdin] [--index-info] [--unresolve] [--ignore-missing] [-z] [--verbose] [--] <file>...";
 
 static unsigned char head_sha1[20];
 static unsigned char merge_head_sha1[20];