Document the two-step approach to run Falco with docker

[leodido]

/area documentation

What would you like to be added:

A snippet showing how to install the Falco drivers via the Falco docker image in a two-step fashion. One, privileged, just to compile or download (from the Drivers Build Grid) and install the driver, and the second one to run Falco.

Why is this needed:

falcosecurity/falco#1158

[leogr]

I believe this has been solved with:

• https://falco.org/docs/installation/#install-driver
• https://falco.org/docs/running/#docker-least-privileged