update readme with tuna reference

openbb_sdk/sdk/core/README.md

@@ -26,6 +26,7 @@
   - [5. REST API](#5-rest-api)
   - [5.1 Test users](#51-test-users)
   - [6. Front-end typing](#6-front-end-typing)
+  - [7. Performance](#7-performance)
 
 ## 1. Introduction
 
@@ -418,3 +419,17 @@ openapi-typescript + openapi-fetch
 openapi-generator
 
 - <https://fastapi.tiangolo.com/advanced/generate-clients/>
+
+## 7. Performance
+
+We aim to have a short import time. To measure that we use `tuna`.
+
+- https://pypi.org/project/tuna/
+
+To visualize the import time breakdown by module, run the following commands from `openbb_sdk` directory:
+
+```bash
+pip install tuna
+python -X importtime openbb/__init__.py 2> import.log
+tuna import.log
+```