Finalize open-sourcing of repository

[jpraynaud]

Issue

Following open sourcing of the repository, we need to finalize some tasks

Tasks

• [x] Make Docker repository public (mithril-client)
• [ ] Curate Github roadmap
• [x] Add missing comments in repository code for Rust (add #![warn(missing_docs)] in lib.rs and main.rs files)
• [ ] Align/Clean README (sub sections only)
• [x] Clean repository unused/stale branches (see)
• [ ] Update the logo
• [ ] Prepare 1' video of the devnet demo
• [x] Create discord channel on IOG server and add it in the documentation
• [ ] Publish on crates.io
• [x] Add visitors statistics tag on explorer website