Update license API docs [ci skip]

doc/api/license.md

 # License
 
-## Retrieve information about the current license
-
-In order to retrieve the license information, you need to authenticate yourself
+In order to interact with license endpoints, you need to authenticate yourself
 as an admin.
 
+## Retrieve information about the current license
+
 ```
 GET /license
 ```
@@ -21,4 +21,37 @@ GET /license
   "user_limit": 100,
   "active_users": 60
 }
-```
\ No newline at end of file
+```
+
+## Add a new license
+
+```
+POST /license
+```
+
+| Attribute | Type | Required | Description |
+| --------- | ---- | -------- | ----------- |
+| `license` | string | yes | The license string |
+
+```bash
+curl -X POST -H "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" "https://gitlab.example.com/api/v3/license?license=eyJkYXRhIjoiMHM5Q...S01Udz09XG4ifQ=="
+```
+
+Example response:
+
+```json
+{
+  "starts_at": "2015-10-24",
+  "expires_at": "2016-10-24",
+  "licensee": {
+    "Name": "John Doe",
+    "Company": "Doe, Inc.",
+    "Email": "john@doe.com"
+  },
+  "user_limit": 100,
+  "active_users": 60
+}
+```
+
+It returns `201` if it succeeds or `400` if failed with an error message
+explaining the reason.

doc/api/licenses.md → doc/api/license_templates.md

-# Licenses
+# License Templates
 
 ## List license templates