Roles: add sample readme

Author: andreyaksenov

doc/code_snippets/snippets/config/instances.enabled/application_role_http_api/README.md

@@ -0,0 +1,22 @@
+# HTTP API
+
+A sample application showing how to implement a custom `http-api` role.
+
+## Running
+
+To start an application, execute the following command in the [config](../../../config) directory:
+
+```console
+$ tt start application_role_http_api
+```
+
+## Making test requests
+
+To test the API, make the following requests:
+
+```console
+$ curl -X GET --location "http://0.0.0.0:8080/band?limit=7" \
+    -H "Accept: application/json"
+$ curl -X GET --location "http://0.0.0.0:8080/band/5" \
+    -H "Accept: application/json"
+```