feat: fix missing initial var in useRef and how to doc

[holaontiveros]

While converting the gradebook application I was running in some issues

• Use ref expected 1 argument

This just needs a default value like null to be type safe, it does work without it but TS will complain big time under many conditions, so having a default value prevents that.

• Nested routes not showing anything, but root path working

The how to had instructions for adding the scripts to run the app in dev mode but was missing a critical part to mark the base route that would be used so webpack can do it's magic

This PR fixes both and should be pretty straightforward

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[arbrandes]

Looks good, thanks!