chore: crosslink from the 0.21.x -> 1.0 docs

[CalMacCQ]

Crosslinking to the v1 preview docs so people can navigate to the v1 docs from docs.quantinuum.com/guppy (currently showing 0.21.16).

I think this is better as an "external link" rather than a crossreference as we have two sphinx sites which we build one at a time. If wer make a crossreference we will get sphinx warnings and the link checker will also complain.

I can also make a PR into main linking to the v0.x docs

[sburton84]

Is it possible to use a relative URL, i.e. just /guppy-v1.x/getting_started.html instead of including the docs.quantinuum.com? Otherwise even on the staging/testing deployments the URL will continue to point to the v1 docs on the production site.

[CalMacCQ]

Ah I didn't think of that. Good point. Let me check.

[CalMacCQ]

I don't think a relative link in the TOC will work here. Basically Sphinx treats this as a non-existing document and doesn't render the sidebar entry

WARNING: toctree contains reference to nonexisting document 'guppy-v1.x/getting_started' [toc.not_readable

We could maybe create a dummy v1_preview.md file with a redirect if need be? I believe sphinx allows you to write a raw html directive

https://stackoverflow.com/questions/50565770/how-to-embed-html-or-xml-in-restructuredtext-sphinx-so-the-browser-can-render

This could be annoying as IDK if we could test it locally.

[CalMacCQ]

Another alternative would be to do a sed replace on the html for staging (changing the absolute url) after we've built the pages. Definetly a hack though.