Update overview link (#6396)

README.md

@@ -7,7 +7,7 @@ and performant applications that focus on multi-party compute and data.
 
 ## Get Started with CCF
 
-- Read the [CCF overview](https://ccf.microsoft.com/) and get familiar with [CCF's core concepts](https://microsoft.github.io/CCF/main/overview/what_is_ccf.html)
+- Read the [CCF overview](https://microsoft.github.io/CCF/main/overview/index.html) and get familiar with [CCF's core concepts](https://microsoft.github.io/CCF/main/overview/what_is_ccf.html)
 - [Install](https://microsoft.github.io/CCF/main/build_apps/install_bin.html) CCF on Linux
 - Get familiar with CCF core developer API with the [template CCF app](https://github.com/microsoft/ccf-app-template)
 - Quickly build and run [sample CCF apps](https://github.com/microsoft/ccf-app-samples)