This allows a COS shell to remotely control another shell from a
serial line. It's very crude now, but the plan is to add tools much
like the POSIX tools, but for COS.

Recipes contain bits and pieces of hardware-related knowledge, but
these bits feel sparse. I've been wanting to consolidate hardware-
related documentation for a while, but always fell at odds with the
recipes organisation.

We don't have recipes anymore, just a /doc/hw section that contains
hardware-related documentation which often translate to precise
instructions to run Collapse OS on a specific machine.

With this new organisation, I hope to end up with a better, more
solid documentation.

I've changed my mind about having documentation in-system. It doesn't
serve much of a purpose and make blkfs significantly heavier.

This commit is the first step in writing a documentation outside of
the blkfs.