Clarify comment about nonce space for Note Encryption

src/zcash/NoteEncryption.hpp

@@ -37,8 +37,8 @@ public:
     }
 
     // Encrypts `message` with `pk_enc` and returns the ciphertext.
-    // This can only be called twice for a given instantiation before
-    // the nonce-space runs out.
+    // This is currently only called twice for a given instantiation; 
+    // but can be called 255 times before the nonce-space runs out.
     Ciphertext encrypt(const uint256 &pk_enc,
                        const Plaintext &message
                       );