Ubuntu 22.04 is recommended for Docker builds, and virtually required
for manual builds.
New devs should use Docker unless they really know what they're doing
and why. They need not have any past Docker experience; JELOS makes it
trivial to use.
Don't maintain the same list in two places.
After careful review, the only packages listed in the help doc that
weren't in the Dockerfile were
- ca-certificates
- gnupg
- qemu-user-static
The first two are only needed to install Docker, and thus do not belong
in the manual build section. The last doesn't appear to be needed for
building, since the Docker container doesn't have it.
