Fixed broken docs links plus a few syntax improvements

Created by: ryan-blunden

The docsite check command has missed a good deal of broken links over time and this PR fixes them.

These were found serving the markdown files from a local http server, then running the macOS app Integrity against it until all broken links were fixed.

Obviously doing this manually is not sustainable, but a similar automated approach may be preferable so broken link and image checking could be decoupled and therefore removed from docsite.