README: document `uuid` and `generate` (#355)
README: document `uuid` and `generate` (#355)

This commit also:
- Synchronizes the help message in the README with the output
  of `configlet --help` (`generate` was missing)
- Alters the headers to be command names, which might be clearer.

Co-authored-by: Erik Schierboom <6e321e24be838c7616721fdb824f9c65569cbfd8@hotmail.com>

exercism/configlet