Add expanded description for the processors tab

You are right, there's probably some confusion around this currently, a more detailed description certainly sounds like a good idea.
However, my preference for this would be to add it to the corresponding handbook page (along with an explanation of the D7/D8 change) and then link to it at the top of the page. This would make it easier to maintain (though, of course, currently no-one really takes care of the handbook) and avoid the large text there in the UI and in the code. (We could then also link to it in the Tour we might want to add.)

I have now added the documentation page. A link to this should now be added, I'd say, to the help text for the "Processors" tab and to its tour. Or, probably the latter is unnecessary if it's already on the page?

Here is a patch adding the link to the introduction text of the "Processors" tab.

This is a nice improvement.

Wow, almost five years for such a simple issue, and more than half of that just for adding the link …
Thanks a lot, Cedric, for finally taking care of this for us! Looks great!
Committed. Thanks again!