New home for in-toto adoptions and integrations

[Aditya Sirish A Yelgundhalli]

Hello everyone,

We've retired our old integrations page on the website in favour of an
in-toto/friends repository where we can better detail adoption and
integration stories. The repo is now live and can be found at
https://github.com/in-toto/friends. Please feel free to share how you're
using in-toto by opening a pull request!

Thanks,
Aditya