Add @app to the Page Guide

[mtanco]

Is your feature request related to a problem? Please describe

The @app('/') feature is explained in the API section of the docs (https://wave.h2o.ai/docs/api/server#app), but is only really find-able if someone is looking for it. When users are on the Pages section of the Guide (https://wave.h2o.ai/docs/pages/) it might be nice for them to explicitly learn about @app() as this is a shortcut for sending apps to a specific page.

Describe the solution you'd like

Add a brief sentence and code snippet to the Pages Guide: https://wave.h2o.ai/docs/pages/

Right after the code for To reference the current page in a Wave app, use q.page.. Here is a first-pass suggestion

To reference a specific page in a Wave app, use the `@app(/foo)` decorator

~
@app('/foo')
async def serve(q: Q):
    page = q.page
~

[tuhinmallick]

Is this issue still open, if yes i would like to work on it

[akhilk2802]

Would like to work on this, please assign