Document Semantic Versioning Best Practice

Git offers semantic versioning - https://github.com/marketplace/actions/git-semantic-version

Not sure the most non-technical explanation of this but perhaps - https://medium.com/swlh/automatic-semantic-versioning-by-using-gitversion-9e22edecb116

Given that the important thing is to align with products and services, we should think through a few common scenarios and document them.

## Dev versions
Many accessibility issues are identified and fixed in alpha, git or development versions of the code, prior to a formal release. If the issue queues are integrated with an OPAT then we are going to see issues which are on versions which are not yet fully baked.

## Issues found post-release
It's normal to get users reporting issues against a particular release of the software. The bug might exist in version 2.3.2.1 but was mitigated in one way or another in 2.3.3.0. Either way, it is useful to add a bug to the earlier release so that it can be included in a comprehensive ACR.

## SASS
It could be that there are multiple versions which have some differences between them which we would want to capture.