(short) documentation for the testgit remote helper

While it's not a command meant to be used by actual users (hence, not
mentionned in git(1)), this command is a very precious help for
remote-helpers authors.

The best place for such technical doc is the source code, but users may
not find it without a link in a manpage.

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Acked-by: Sverre Rabbelier <srabbelier@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-remote-helpers.txt

@@ -362,6 +362,8 @@ SEE ALSO
 --------
 linkgit:git-remote[1]
 
+linkgit:git-remote-testgit[1]
+
 GIT
 ---
 Part of the linkgit:git[1] suite

Documentation/git-remote-testgit.txt

@@ -0,0 +1,30 @@
+git-remote-testgit(1)
+=====================
+
+NAME
+----
+git-remote-testgit - Example remote-helper
+
+
+SYNOPSIS
+--------
+[verse]
+git clone testgit::<source-repo> [<destination>]
+
+DESCRIPTION
+-----------
+
+This command is a simple remote-helper, that is used both as a
+testcase for the remote-helper functionality, and as an example to
+show remote-helper authors one possible implementation.
+
+The best way to learn more is to read the comments and source code in
+'git-remote-testgit.py'.
+
+SEE ALSO
+--------
+linkgit:git-remote-helpers[1]
+
+GIT
+---
+Part of the linkgit:git[1] suite

git-remote-testgit.py

@@ -1,5 +1,18 @@
 #!/usr/bin/env python
 
+# This command is a simple remote-helper, that is used both as a
+# testcase for the remote-helper functionality, and as an example to
+# show remote-helper authors one possible implementation.
+#
+# This is a Git <-> Git importer/exporter, that simply uses git
+# fast-import and git fast-export to consume and produce fast-import
+# streams.
+#
+# To understand better the way things work, one can activate debug
+# traces by setting (to any value) the environment variables
+# GIT_TRANSPORT_HELPER_DEBUG and GIT_DEBUG_TESTGIT, to see messages
+# from the transport-helper side, or from this example remote-helper.
+
 # hashlib is only available in python >= 2.5
 try:
     import hashlib