Documentation updates and other to-do items

Discussion outcomes from meeting with @pinamont @tdado @maly:

• improve documentation for how-to-setup: make it clear how StatAnalysis works / list that first, say what setup does exactly

• add a page with an overview of how to use multifit

• move most of the content from the readme over to the website, especially

  • actions which exist
  • CLI

• CI tests against latest xRooFit version to catch potential issues early (nightly / weekly?)

• Add a page aimed at advanced users or developers. Can document histogram suffix meanings and workspace creation option as described in !1471 (merged).