Update README and Contribution Guide
What does this MR do?
Improve the top-level Markdown files, to target first-time users of DORiE.
- Add table of contents
- Improve installation instructions & dependency overview
- Update usage instructions
- Make guidelines for contributing more encouraging for external users
- Add a bit of information on how to use GitLab
Is there something that needs to be double checked?
Can this MR be accepted?
- Added/Updated documentation
- Pipeline passing
- Squash option set
- Delete branch option set
[ ] Added entry to