Documentation: inject the current git revision into the website

Change-Id: I79cceca7373f8bdf9bbfba5d84b8fa589afa838b
Signed-off-by: Patrick Georgi <patrick@georgi.software>
Reviewed-on: https://review.coreboot.org/26897
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Philipp Deppenwiese <zaolin.daisuki@gmail.com>
diff --git a/Documentation/conf.py b/Documentation/conf.py
index 8fde81e..b8415c6 100644
--- a/Documentation/conf.py
+++ b/Documentation/conf.py
@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+import subprocess
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']
@@ -18,10 +19,10 @@
 # |version| and |release|, also used in various other places throughout the
 # built documents.
 #
-# The short X.Y version.
-version = u'4.7'
 # The full version, including alpha/beta/rc tags.
-release = u'4.7' # TODO: use 'git describe'
+release = subprocess.check_output(('git', 'describe'))
+# The short X.Y version.
+version = release.split("-")[0]
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.