git-archive: document --exec

Signed-off-by: Michele Ballabio <barra_cuda@katamail.com>
Signed-off-by: Lars Hjemli <hjemli@gmail.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

Documentation/git-archive.txt

@@ -10,7 +10,8 @@ SYNOPSIS
 --------
 [verse]
 'git-archive' --format=<fmt> [--list] [--prefix=<prefix>/] [<extra>]
-	      [--remote=<repo>] <tree-ish> [path...]
+	      [--remote=<repo> [--exec=<git-upload-archive>]] <tree-ish>
+	      [path...]
 
 DESCRIPTION
 -----------
@@ -52,6 +53,10 @@ OPTIONS
 	Instead of making a tar archive from local repository,
 	retrieve a tar archive from a remote repository.
 
+--exec=<git-upload-archive>::
+	Used with --remote to specify the path to the
+	git-upload-archive executable on the remote side.
+
 <tree-ish>::
 	The tree or commit to produce an archive for.