Extend documentation. Add certificates and services.

[hscheid]

Dear @ddobrigk and @vkucera
I extended the documentation by adding

• Information about registration in ALICE
• Genertation and registration of certificates

Both are based on the old documentation here https://alice-doc.github.io/alice-analysis-tutorial/start/
Let me know if you are missing something.

[vkucera]

Thanks @hscheid
Can you please fix the markdownlint errors and the trailing spaces?

[hscheid]

Fixed. Links work, false positives. Might need investigation.

[vkucera]

Fixed. Links work, false positives. Might need investigation.

Thanks. Yes, the link errors are irrelevant.