add badges for the latest release and the CIs (!178)

this adds three badges to the README:
- the latest release (links to the [release page](https://gitlab.isae-supaero.fr/dragoon/komodo/-/releases))
- the GitLab CI status (links to the [GitLab pipeline dashboard](https://gitlab.isae-supaero.fr/dragoon/komodo/-/pipelines))
- the GitHub CI status (links to the [GitHub workflow runs dashboard](https://github.com/dragoon-rs/komodo/actions))

README.md

 # Komodo: Cryptographically-proven Erasure Coding
 
+[![release](https://gitlab.isae-supaero.fr/dragoon/komodo/-/badges/release.svg)](https://gitlab.isae-supaero.fr/dragoon/komodo/-/releases)
+[![source](https://gitlab.isae-supaero.fr/dragoon/komodo/badges/main/pipeline.svg?key_text=GitLab%20CI)](https://gitlab.isae-supaero.fr/dragoon/komodo/-/pipelines)
+[![mirror](https://github.com/dragoon-rs/komodo/actions/workflows/ci.yml/badge.svg)](https://github.com/dragoon-rs/komodo/actions)
+
 ## the library
 see `cargo doc` or [the library itself](src/)