Sidecar documentation

[ipopescu]

When the sidecar repo goes public......

Pre-requisites:

• [x] the casper-sidecar repository is public
• [ ] there is a link to the Debian package to install the sidecar on the node => waiting on this. I can test locally with nctl
• [ ] the docs are in this branch: https://github.com/casper-network/docs/tree/feat-sse_sidecar => will be moved to feat-2.0_docs

Acceptance criteria:

• [x] Update the sidecar READMEs and examples (edit, flow)
• [ ] Update docs repository with sidecar content
• [ ] Address TODOs related to adding links in the docs
• [x] Consolidate README files in the repository and reduce any duplication in the GitHub README and resources/ETC_README.md.