docs: make header image clickable in README.md

Author: Pierre

README.md

@@ -1,6 +1,6 @@
 # Python SDK for WorkflowAI
 
-![WorkflowAI](./examples/assets/readme-header.png)
+[![WorkflowAI](./examples/assets/readme-header.png)](https://workflowai.com)
 
 [![PyPI version](https://img.shields.io/pypi/v/workflowai.svg)](https://pypi.org/project/workflowai/)