Link to GitHub tskit-dev project site

[hyanwong]

I was looking for a generic link to https://github.com/tskit-dev from the top of the software page, but couldn't find it - only links to each specific repo.

[benjeffery]

What purpose do you see promoting that page serving? I don't want to give the impression that that page is a list of tree sequence software for example.

[hyanwong]

I wouldn't want to "promote" the page, but it's useful for people nosing around to know that it exists. I use it as a shortcut to the various GitHub repos I want to look at. But perhaps that's just me.

[benjeffery]

Maybe it is worth having a paragraph somewhere about what the tskit-dev org actually is and means? That would be the place for that link to go.