The original dEQP.md covered Windows pretty well, but was confusing to
follow on Linux. So I've fleshed out the Linux process to be as complete
as the Windows process.

Change-Id: I8373e56db7d8d74bf5bcdfc7c7d23b740a11c25a
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/28369Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Sean Risser <srisser@google.com>