Crate a list of essential How-To guides

[jleibs]

List of guides / stub pages go here: https://github.com/rerun-io/rerun-docs/blob/main/docs/how-to-guides.md

[jleibs]

Add a link to an issue/form for requesting new how-to guides.

[Wumpf]

Dropped from launch-day documentation, but we still want to add such guides!

[emilk]

We have these now: https://www.rerun.io/docs/howto