docs for user management (+ general doc update)
With the merge of #25 (closed) it is now possible to add new users and modify some basic parameters for them. We need docs update to reflect those changes.
Other doc changes:
- Add pointer to stork.readthedocs.io in README.md
- Intro section (remove PDF, TXT)
- Stork backend API update
- Add a section about agent API
- How to deploy stork-agent