Last minute language nit on clear signing

Squeaking in under the wire.

Section 7, Cleartext signature framework says:

    It is desirable to sign a textual octet stream without ASCII
    armoring the stream itself, so the signed text is still readable
    without special software.

Suggest "It is sometimes desirable to sign ..."

(i.e. add a "sometimes".  It's not always desirable to clearsign).

David