README needs heavy rewriting

[jagerman]

Someone trying to get oxend to build on an ancient machine (i.e. xenial) recently contacted me and reported being quite mislead by some of the info in our README; looking at it we have some up-to-date info, but also a ton of outdated stuff that hasn't really changed from when Monero was forked.

[darcys22]

Agree, think we also lost some information between dev becoming the main branch and the readme that was on the master branch