ssh: improve docs on Certificate.SignCert
Document the fact that SignCert sets the Nonce field.  This makes it
clear that callers need not set it themselves.
Original change by Jakob Weisblat in CL 57051.
Fixes golang/go#21384
@@ -414,8 +414,8 @@ func (c *CertChecker) CheckCert(principal string, cert *Certificate) error {
return nil
}
-// SignCert sets c.SignatureKey to the authority's public key and stores a
-// Signature, by authority, in the certificate.
+// SignCert signs the certificate with an authority, setting the Nonce,
+// SignatureKey, and Signature fields.
func (c *Certificate) SignCert(rand io.Reader, authority Signer) error {
c.Nonce = make([]byte, 32)
if _, err := io.ReadFull(rand, c.Nonce); err != nil {
