Update the Zephyr document to provide more detailed instructions, and add info
about espressif toolchain too.
Add ESP32C3 (RISC-V) and Particle Argon boards support to the zephyr platform
sample. More boards are possible, but the script doesn't scale well and is to be
improved in future.
Add Dockerfile to kickstart a Zephyr development environment as it can be rather
confusing for new users.
