Update user roles list API documentation

awx/api/templates/api/user_roles_list.md

@@ -0,0 +1,12 @@
+# List Roles for this User:
+
+Make a GET request to this resource to retrieve a list of roles associated with the selected user.
+
+{% include "api/_list_common.md" %}
+
+# Associate Roles with this User:
+
+Make a POST request to this resource to add or remove a role from this user. The following fields may be modified:
+
+   * `id`: Required. The Role ID to add to the user. 
+   * `disassociate`: Optional. Provide if you want to remove the role.