Added recommendation to use Purpur to wiki

[alethkit]

Since doom has a high proportion of resources consumed by Minecraft servers, I have added a suggestion to the wiki to use https://purpurmc.org/, which should allow for reduced congestion on doom (and hopefully better TPS).

[eleanor-clifford]

Perhaps we should word this more as a suggestion to try rather than recommendation, unless someone who has experience running both can comment?

[eleanor-clifford]

Actually, this should probably primarily be an edit to /tutorials/others/simple-minecraft-server/ (although maybe with a minor change on this page too), and we'd have to make sure that that the tutorial is edited to work with Purpur/Paper (or, preferably, have two versions of the tutorial, since some users will still want to use vanilla)