Refresh the "pc-bios/README" file with edk2, OpenSSL, and Berkeley
SoftFloat release info, matching the edk2-stable201905 firmware images
added in the previous patch.

Cc: Philippe Mathieu-Daud <philmd@redhat.com>
Ref: https://bugs.launchpad.net/qemu/+bug/1831477


Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Philippe Mathieu-Daud <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daud <philmd@redhat.com>