Set out versioning and updates guidance

[jatkinson1000]

With the publication in JOSS we made our first release v1.0.0

We should discuss how we now want to proceed with releases.

My preference would be selecting appropriate points and adding a tag+release rather than automating anything to bump at every commit to main.

Suggestion would be:

• Add guidance of versioning to docs
  • major for API changes, minor for periodic releases of new features, patch for bugfixes following https://semver.org/
• Create a changelog following https://keepachangelog.com/en/1.0.0/ that users/maintainers should update as appropriate with each pull request