[Minor] The image link URLs are no longer working.

[TelicentPaul]

Better to use the local equivalents.

[paulc-dstl]

Just catching up on github, noticed this is lurking. Does this just require commits to be signed to fix...? @TelicentPaul @afizzycola https://docs.github.com/en/authentication/managing-commit-signature-verification/signing-commits