doc(pillar/git): document setting custom root

doc/topics/tutorials/gitfs.rst

@@ -228,18 +228,26 @@ following to your master config file:
 .. code-block:: yaml
 
     ext_pillar:
-      - git: <branch> <repo>
+      - git: <branch> <repo> [root=<gitroot>]
 
 
 The ``<branch>`` param is the branch containing the pillar SLS tree, and the
 ``<repo>`` param is the URI for the repository. The below example would add the
-``master`` branch of the specified repo as an external pillar source.
+``master`` branch of the specified repo as an external pillar source:
 
 .. code-block:: yaml
 
     ext_pillar:
       - git: master https://domain.com/pillar.git
 
+If you would like to use the pillars from a subdirectory of the GIT repository,
+you can set the ``root`` parameter:
+
+.. code-block:: yaml
+
+    ext_pillar:
+      - git: master https://domain.com/pillar.git root=subdirectory
+
 More information on the git external pillar can be found :mod:`here
 <salt.pillar.git_pillar>`.
 

salt/pillar/git_pillar.py

@@ -8,7 +8,10 @@ so:
 .. code-block:: yaml
 
     ext_pillar:
-      - git: master git://gitserver/git-pillar.git
+      - git: master git://gitserver/git-pillar.git root=subdirectory
+
+The `root=` parameter is optional and used to set the subdirectory from where
+to look for Pillar files (such as ``top.sls``).
 
 Note that this is not the same thing as configuring pillar data using the
 :conf_master:`pillar_roots` parameter. The branch referenced in the