Fix docs link to `hideSpinner` and `showSpinner`

[reynaldichernando]

if you try to click the hideSpinner or the showSpinner page in https://docs.puter.com/UI/#additional-ui-elements it will get a 404
the fix should be fairly simple, by adding these pages to the sidebar, since that controls which page is built

[Rajat1472]

I want to work on this.

[reynaldichernando]

hi @Rajat1472 , assigned!