Add edit on github link to documentation pages

Signed-off-by: Julius Härtl <jus@bitgrid.net>

conf.py

@@ -1,6 +1,11 @@
 # global configuration for every documentation added at the end
 
-import os
+import os, sys
+
+dir_path = os.path.dirname(os.path.realpath(__file__))
+sys.path.insert(0, os.path.abspath(dir_path + '/_ext'))
+
+extensions = ['edit_on_github']
 
 # General information about the project.
 copyright = u'2012-2017, The Nextcloud developers'
@@ -14,7 +19,6 @@ version = '13'
 # The full version, including alpha/beta/rc tags.
 release = '13'
 
-
 # substitutions go here
 rst_epilog =  '.. |version| replace:: %s' % version
 
@@ -22,3 +26,6 @@ html_context = {
 	'doc_versions': ['11', '12', '13'],
 	'current_doc': os.path.basename(os.getcwd()),
 }
+
+edit_on_github_project = 'nextcloud/documentation'
+edit_on_github_branch = 'master'