add entrypoint hooks and function to add config sources

[sneakers-the-rat]

fix: #67

• function
• entrypoints
• tests
• docs

[coveralls]

coverage: 85.299% (-0.01%) from 85.312%
when pulling a4ebabe on error-tracebacks
into ab4dd8e on main.

[sneakers-the-rat]

oop i pushed this from the wrong branch, accidentally did gti switch, but it's fine

[sneakers-the-rat]

pushed the docs part to #87 , otherwise ready 2 go