Updated HADDOCK3 installation instructions in tutorials

[amjjbonvin]

Added link to the registration form and modified installation instructions link to point to the haddock3 user manual.

[AnnaKravchenko]

I am wondering why we even send people to the GitHub repo if all the instructions are on the wiki.

I.e., I can envision users opening GitHub, opening the wiki, and getting confused by instructions in the README on GitHub vs instructions on the wiki. Maybe it’s better to point only to the wiki? Especially since it also contains a link to the GitHub repo.

[amjjbonvin]

We could only leave the link to the registration (nice to have for statistics/reporting purposes) and the installation instructions and remove the git repo here.

[AnnaKravchenko]

We could only leave the link to the registration (nice to have for statistics/reporting purposes) and the installation instructions and remove the git repo here.

I think this would be best.
Tech-savvy users likely will go to GitHub prior to checking tutorials anyway

[amjjbonvin]

Updated!