Change Gumroad link to include EPUB option

Updated Gumroad link to include EPUB format.

Author: Siddhant-K-code

README.md

@@ -2,7 +2,7 @@
 
 Concepts, workflows, and team practices for AI agent infrastructure. 10 parts, 33 chapters, 4 appendices.
 
-[![Build with Ona](https://ona.com/build-with-ona.svg)](https://app.ona.com/#https://github.com/Siddhant-K-code/agentic-engineering-guide) [![Get the PDF on Gumroad](https://img.shields.io/badge/Gumroad-Get_the_PDF-ff90e8?style=flat&logo=gumroad&logoColor=000)](https://siddhantkhar5.gumroad.com/l/agentic-engineering-guide)
+[![Build with Ona](https://ona.com/build-with-ona.svg)](https://app.ona.com/#https://github.com/Siddhant-K-code/agentic-engineering-guide) [![Get the EPUB / PDF on Gumroad](https://img.shields.io/badge/Gumroad-Get_the_PDF-ff90e8?style=flat&logo=gumroad&logoColor=000)](https://siddhantkhar5.gumroad.com/l/agentic-engineering-guide)
 
 **Read online:** [agents.siddhantkhare.com](https://agents.siddhantkhare.com)