Update Readme.md and create changelog.md and contributing.md docs

[EwoutH]

Update some of the documentation, specifically:

• Update Readme with general information (Update Readme with an introduction and documentation, installation and contribution sections #199)
• Create changelog.md based on previous release notes (Create release.yml file for automatic release notes generation #152 and Bump version and update changelog for 2.2.0 release #159)
• Create contributing.md on how to contribute and tag releases (Create initial CONTRIBUTING.md documentation #162)