Create user documentation for using SSH devices

We want some clear documentation on what users need to do, to be able to make use of the ssh device/toolchain.

There are some details on the Bazel setup required to use the toolchain in the description of MR !107 (merged).

The documentation should explain:

• Required setup in terms of platform.
• How to create a target that makes use of this new platform.
• How to run the example target, showing how to make use of the CLI flags.

The documentation will assume:

• The user already has a device that they want to communicate with.
• The user knows how to use bazel.
• The user already has their Bazel Module setup to be able to make use of rules_labgrid.