Spline docs and getting started version mismatch

[cerveada]

https://absaoss.github.io/spline/0.5.html links to here, but version used here is 0.6

[wajda]

Just an idea - we could create a branch per every major agent+core+ui version combination and refer that branch from the GH pages. We could also maintain a list of alive branches in the README head, so that even if the user lands on the most recent "develop" README version he or she will immediately see the refs to the other ones.