DownloadExtraInfo doesn't download bridge extra infos

There's some confusion about what these options do for bridge extra infos:

DownloadExtraInfo 1
FetchUselessDescriptors 1

We should clarify that they don't affect Tor's usual behaviour, which is to (eventually) download bridge descriptors, and never download bridge extra-infos.

Or we should make them download bridge extra-infos, and document that.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information