fix: docs portal link (#102)

quick-start.md was linked to the previous notion-based documentation
portal.

This fix changes the link to the current documentation portal aka
[docs-hub](https://docs.fuel.network/)

book/src/quick-start.md

@@ -65,6 +65,6 @@ Packages chapter**](./packages.html).
 For more details on installing Nix or configuring an existing Nix or NixOS
 installation, see [**the Nix Setup chapter**](./nix-setup.html).
 
-If you are content with the installation, see
-[**The Documentation Portal**](https://www.notion.so/fuellabs/Documentation-Portal-V1-0-Beta)
+If you are content with the installation, see the
+[**Documentation Portal**](https://docs.fuel.network/)
 for more details on how to build with Fuel!