Documentation for Customising HTML Email Templates

[csmith-he]

brief description of changes

Documentation explaining how to use the new functionality allowing the customisation (branding) of emails in an Arches instance

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• [X] the PR branch was originally made from the base branch

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• [ ] after these changes the docs build locally without error

This box should only be checked you intend to follow through on it (we can do it on our end too)

• [ ] I will cherry-pick all commits in this PR into other branches that should have them after this PR is merged

[csmith-he]

@ekansa - This is a first pass at the documentation on email customisation. Please could you take a look and let me know if anything isn't clear/is missing? Thanks!

[csmith-he]

I pushed a commit with minor style updates. I also changed the spelling to the US spelling variant "customize", but I noted the UK version of the spelling in the text so it should still appear in searches.

I don't think we have a hard and fast rule about spelling, but I think for consistency, we'll keep with US spelling preferences (since that seems to be the established pattern in these docs).

Beyond that THANK YOU! This is going to be very helpful, and I really appreciate the link to the Accessibility discussion as well.

PS. If you think my edits are OK, please let me know, and then I'll merge your branch into the official docs.

I'm very happy with the changing of the spelling (I agree that consistency of spelling across the docs is a good thing). I'm happy for this to be merged into the official docs.