Update zuulv3 spec to include job repo information

This has been discussed but was accidentally omitted from the spec.

Change-Id: Id3c81ab337d4df0c81b33c873883ecb1846a1855

specs/zuulv3.rst

@@ -286,12 +286,25 @@ have multiple aspects to accomodate differences among branches, etc.::
       branches: stable/juno  # Could be combined into previous with regex
       nodes: precise         # if concept of "best match" is defined
 
+Jobs may specify that they use other repos in the same tenant, and the
+launcher will ensure all of the named repos are in place at the start
+of the job::
+
+  ### global_config.yaml (continued)
+  - job:
+      name: devstack
+      parent: base
+      repos:
+        - openstack/nova
+        - openstack/keystone
+        - openstack/glance
+
 Jobs may specify that they require more than one node::
 
   ### global_config.yaml (continued)
   - job:
       name: devstack-multinode
-      parent: base
+      parent: devstack
       nodes: multinode
 
 Jobs defined centrally (i.e., not in-repo) may specify auth info::