Add codeblocks for debian repo

[ann0see]

Short description of changes Related to https://github.com/jamulussoftware/jamuluswebsite/pull/938#discussion_r1278308306 copy and paste should be easy for installing the repo:

Context: Fixes an issue? Related issues Related to comment by @mcfnord https://github.com/jamulussoftware/jamuluswebsite/pull/938#discussion_r1278308306

Status of this Pull Request Ready for review

What is missing until this pull request can be merged? /

Does this need translation? YES

Checklist

• [x] I've verified that this Pull Request follows the general code principles
• [ ] I waited some time after this Pull Request was opened and all GitHub checks completed without errors.
• [ ] I'm sure that this Pull Request goes to the correct branch

[mcfnord]

I was totally gonna do this one. Way better.

[ann0see]

I believe the weblate PR should be merged before anything else.