docs: add CNAME

[michalsn]

Description Add CNAME to the docs, so it can be deployed every time to the gh-pages branch.

Checklist:

• [x] Securely signed commits
• [ ] Component(s) with PHPDoc blocks, only if necessary or adds value
• [ ] Unit testing, with >80% coverage
• [ ] User guide updated
• [ ] Conforms to style guide