Minor addition for source link in JSON

This is needed to help with JSON to RST validation

Change-Id: I2ea18a563f2826e25b826cd239cc94cc8140fba0

2015.03.json

@@ -1,6 +1,7 @@
 {
   "id": "2015.03",
   "schema": "1.2",
+  "source": "http://git.openstack.org/cgit/openstack/defcore/",
   "status": "approved",
   "replaces": "2014.07",
   "releases": ["havana", "icehouse"],

2015.04.json

@@ -1,6 +1,7 @@
 {
   "id": "2015.04",
   "schema": "1.2",
+  "source": "http://git.openstack.org/cgit/openstack/defcore/",
   "status": "draft",
   "replaces": "2015.03",
   "releases": ["havana", "icehouse", "juno"],

2015.next.json

@@ -1,6 +1,7 @@
 {
   "id": "2015.next",
   "schema": "1.2",
+  "source": "http://git.openstack.org/cgit/openstack/defcore/",
   "status": "draft",
   "replaces": "2015.04",
   "releases": ["havana", "icehouse", "juno"],

README.rst

@@ -25,7 +25,8 @@ The JSON files have a specific schema to support
 .. code-block:: json
 
   { "id": "2015.03",        # Spec name (date based)
-    "schema": "1.1",        # Schema version
+    "source": "http://git.openstack.org/cgit/openstack/defcore/",   # git repo for files
+    "schema": "1.2",        # Schema version
     "status": "approved",   # can be draft, review or approved
     "replaces": "2014.07",  # previous spec
     "releases": ["icehouse"], # array of releases, lower case