readme: RSA keys must use --bare

[pinheadmz]

See #131 and #126 (comment)

We need to nip this in the bud by requiring RSA key users add --bare to their claim. I suppose we could also rip out the goosig code, but this should suffice for now.

[seidtgeist]

@pinheadmz Anything I can do if I submitted my claim without --bare?

I got this in hsd’s log output after sending the bare base64 string:

[error] (node) Verification failure: txn-already-in-mempool (code=alreadyknown score=0 hash=ac1b13c2dcec18f6e81be8782354acd028b45258d45028500454791066875d35)
[warning] (node) Verification failed for proof: ac1b13c2dcec18f6e81be8782354acd028b45258d45028500454791066875d35.
[warning] (node) Attempting to broadcast anyway...

[pinheadmz]

@seidtgeist #133

[seidtgeist]

@pinheadmz Thank you!