Dead link in README.md

[wyphan]

The link pointing to "LLNL co-design pages" in the Introduction section of README.md is a dead link. Perhaps it can be refreshed to this one instead? https://asc.llnl.gov/codes/proxy-apps/quicksilver

(Also, I don't know who in ECP I should contact for this one, but the same dead link is listed in https://proxyapps.exascaleproject.org/app/quicksilver/ )

[utsav-mishra]

I see this is not picked. Can I take this?