Fix inner docs site link

The link to the overview doc, which is also on the public docs site, was
using the markdown syntax. This changes the link to use the jekyll syntax.

docs/walkthrough.md

@@ -23,7 +23,7 @@ to each other using Aranya Fast Channels. There are a few things to keep in mind
   protected partition, such as an HSM, for maximum security. This avoids a
   single access point for all Aranya user keys in case a machine is compromised.
 
-See the [examples](https://github.com/aranya-project/aranya/tree/main/examples/) directory for example applications that follow scenarios similar to the one described in this document. Also, see the [overview documentation](aranya-overview.md) for more details on the components used in this walkthrough.
+See the [examples](https://github.com/aranya-project/aranya/tree/main/examples/) directory for example applications that follow scenarios similar to the one described in this document. Also, see the [overview](https://aranya-project.github.io/aranya-docs/overview/) for more details on the components used in this walkthrough.
 
 # Outline