The existing non-Docker instructions are basically impossible to follow
because the esp-open-sdk does not compile. Update these instructions to
use the exact toolchain that our CI uses.
Also split the Docker from non-Docker instructions, to avoid confusion
about which commands need to be prefixed.
Signed-off-by: Jim Mussared <jim.mussared@gmail.com>
The specific board can be selected with the BOARD makefile variable. This
defaults (if not specified) to BOARD=GENERIC, which is the original default
firmware build. For the 512k target use BOARD=GENERIC_512K.
This is to keep the top-level directory clean, to make it clear what is
core and what is a port, and to allow the repository to grow with new ports
in a sustainable way.