We only want to use an old version for glibc which the centos:7
image takes care of.

The old version of git used in debian:8 was causing problems
with the uid/gid passthrough with no user in passwd.

Much easier for users to use our CI scripts instead of each individual
yarn step.

* Document release branches

* Update doc/CONTRIBUTING.md
Co-authored-by: NAsher <ash@coder.com>
Co-authored-by: NAsher <ash@coder.com>

More clear as discussed in PR.

It is not mentioned that the "release" script requires "jq" to be installed on the system to build code-server releases

Closes #1648

Many random bizarre issues otherwise.

Also includes misc improvements to docs and scripts.

Closes many issues that I'll prune after adding more docs
for users.

For #1306.