split out docs into separate files in the docs folder

[catdad]

• [x] table of contents
• [x] tests file
• [x] cli file
• [x] api file
• [x] link to individual files from README
• [x] contributing guide
• [x] quick start guide

[catdad]

Contribution guide moved to #78.

[catdad]

Published in 0.3.0.