Document /admin

[djanderson]

Django gives us an /admin website that helps change settings and manage the sensor in a graphical way. We're starting to make more use of that and enable changing core settings there, but it hasn't been documented yet.

[djanderson]

Related: the Glossary defines Capability as being often "hard-coded" by the sensor owner. This wording should be changed to something like:

Available actions, installation specifications (e.g., mobile or stationary), and operational ranges of hardware components (e.g., frequency range of SDR). These values are generally entered once by the sensor owner and rarely change.