Updated README for improved DevEx

[suyashcjoshi]

1. Improved Formatting
2. Fixed broken link, badges.
3. Updated getting started with the shell command that is on main Orbital page and mentioned Docker as pre-req.
4. For contact us: right now linked to Slack channel, but can be changed to your email etc
5. Added Table of Contents for readability/scannability, improved wording overall to make it coherent.

TODO:

1. Add product Screenshot/Animated Gif after the upcoming release
2. Add release tag on GitHub after upcoming release

[suyashcjoshi]

Fixed the items flagged in GitLab, will go over with you here @martypitt before sending Merge Request on GitLab. Thanks!