[Admin] configuring for cross-repo includes (#5446)

Author: Rick-Kirkham

.openpublishing.publish.config.json

@@ -110,6 +110,12 @@
       "url": "https://github.com/Microsoft/templates.docs.msft",
       "branch": "main",
       "branch_mapping": {}
+    },
+    {
+      "path_to_root": "reusable-content",
+      "url": "https://github.com/MicrosoftDocs/reusable-content/",
+      "branch": "main",
+      "branch_mapping": {}
     }
   ],
   "branch_target_mapping": {},