Make it easier to find the core source repositories

[duncand]

There doesn’t seem to be any clear way to find the public version control for Rakudo/MoarVM/NQP et al by way of perl6.org.

When I go to https://perl6.org/downloads/ the section on installing from source points to http://rakudo.org/how-to-get-rakudo/ and that points to tarballs with the source, but no repositories.

I happen to know they're on Github but there’s no mention of the actual repositories on either site that I could easily find. This is in contrast to many open source projects where a Github-or-other-repo url is easy to find.

Please make it more obvious on perl6.org where one can see the canonical source repositories for the core parts of the Perl 6 ecosystem.

Thank you.