Update comment

psiphon/common/protocol/serverEntry.go

@@ -293,13 +293,18 @@ func (fields ServerEntryFields) AddSignature(publicKey, privateKey string) error
 
 	delete(copyFields, "signature")
 
+	// Best practise would be to sign the JSON encoded server entry bytes and
+	// append the signature to those bytes. However, due to backwards
+	// compatibility requirements, we must retain the outer server entry encoding
+	// as-is and insert the signature.
+	//
 	// Limitation: since the verifyier must remarshal its server entry before
 	// verifying, the JSON produced there must be a byte-for-byte match to the
 	// JSON signed here. The precise output of the JSON encoder that is used,
 	// "encoding/json", with default formatting, as of Go 1.11.5, is therefore
 	// part of the signature protocol.
 	//
-	// TODO: use a stadard, canonical encoding, such as JCS:
+	// TODO: use a standard, canonical encoding, such as JCS:
 	// https://tools.ietf.org/id/draft-rundgren-json-canonicalization-scheme-05.html
 
 	marshaledFields, err := json.Marshal(copyFields)