Update /update_inventory_sources endpoint documentation

awx/api/templates/api/inventory_inventory_sources_update.md

@@ -0,0 +1,23 @@
+# Update Inventory Sources
+
+Make a GET request to this resource to determine if any of the inventory sources for
+this inventory can be updated. The response will include the following fields for each
+inventory source:
+
+* `inventory_source`: ID of the inventory_source
+  (integer, read-only)
+* `can_update`: Flag indicating if this inventory source can be updated
+  (boolean, read-only)
+
+Make a POST request to this resource to update the inventory sources. The response
+status code will be a 202. The response will contain the follow fields for each of the individual
+inventory sources:
+
+* `status`: `started` or message why the update could not be started.
+  (string, read-only)
+* `inventory_update`: ID of the inventory update job that was started.
+  (integer, read-only)
+* `project_update`: ID of the project update job that was started if this inventory source is an SCM source.
+  (interger, read-only, optional)
+
+{% include "api/_new_in_awx.md" %}