User guide, deployment page: add section 'Deployment on GitHub Pages'

[deining]

This PR adds a new section Deployment on GitHub Pages to the deployment page of the user guide.

You may have a look at the section preview at Netlify here.

The newly added section also refers to the deployment workfile, to be added to the example site via this PR. Both PRs are closely related and should be reviewed in parallel.

Thir PR also brings some minor corrections and amendments to the section Deployment with Netlify.

[LisaFC]

Looks good! I made some small changes to the docs. @geriom or @chalin do you want to take a look? @Logofile I know you're using something GitHub Pages-y for protobuf, any feedback?

[Logofile]

The content looks sound from my experience rolling out protobuf.dev. Thanks for the contribution, Andreas!

[chalin]

Yes, will have a look shortly.

[deining]

Yes, will have a look shortly.

@chalin: friendly ping
I just rebased my PR and resolved existing merge conflicts. My already approved PR is now read for final review and eventual merging. 😄

[deining]

Yes, will have a look shortly.

@chalin: friendly ping I just rebased my PR and resolved existing merge conflicts. My already approved PR is now read for final review and eventual merging. 😄

@chalin: friendly ping again.
Just rebased this PR again and brought all information and versions up to date.
This info was just requested in #1975, so I would really like to see this merged shortly.