Update with pointers to related repos and progress since 2018

[nealmcb]

The README should point to up-to-date information on ColoradoRLA:

• The second phase of development of ColoradoRLA was performed by Democracy Works between
  2018-06-19 and 2019-11-10. Their work is available at https://github.com/democracyworks/ColoradoRLA.
• Subsequently, the Colorado Department of State took over maintenance, and their latest version as of 2022 is at https://github.com/cdos-rla/colorado-rla. That repository should be rebased on top of the one at DemocracyWorks so it has the full version history.

It should also note that the version here is out-of-date and depends on some out-of-date versions of other software which could introduce security vulnerabilities.

[kiniry]

Good points @nealmcb. Being more explicit about what happened later is a good idea.