Update link

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alexellis2@gmail.com>

Author: alexellis

README.md

@@ -122,7 +122,7 @@ Learn about [OpenFaaS templates in the docs](https://docs.openfaas.com/languages
 View our [official training materials](https://docs.openfaas.com/tutorials/training)
 
 ### Official eBook and video workshop
-[![eBook logo](https://www.alexellis.io/serverless.png)](https://gumroad.com/l/serverless-for-everyone-else)
+[![eBook logo](/docs/ebook-cover.png)](https://gumroad.com/l/serverless-for-everyone-else)
 
 The founder of OpenFaaS wrote *Serverless For Everyone Else* to help developers understand the use-case for functions through practical hands-on exercises using JavaScript and Node.js. No programming experience is required to try the exercises.