Improved README with responder example.

Closes #11

README.md

@@ -31,11 +31,16 @@ NoiseBuilder class provides highest level of abstraction for the package. You ca
 through this class' interfaces. An example for setting up NoiseBuilder could look like this:
 
 ```python
+import socket
+
 from noise.builder import NoiseBuilder
 
+sock = socket.socket()
+sock.connect(('localhost', 2000))
+
 # Create instance of NoiseBuilder, set up to use NN handshake pattern, Curve25519 for 
 # elliptic curve keypair, ChaCha20Poly1305 as cipher function and SHA256 for hashing.  
-proto = NoiseBuilder.from_name('Noise_NN_25519_ChaChaPoly_SHA256')
+proto = NoiseBuilder.from_name(b'Noise_NN_25519_ChaChaPoly_SHA256')
 
 # Set role in this connection as initiator
 proto.set_as_initiator()
@@ -47,20 +52,62 @@ proto.start_handshake()
 message = proto.write_message()
 # Send the message to the responder - you may simply use sockets or any other way 
 # to exchange bytes between communicating parties. 
-# For clarity - we omit socket creation in this example.
-sock.send(message)
+sock.sendall(message)
 # Receive the message from the responder 
-received = sock.recv()
+received = sock.recv(2048)
 # Feed the received message into noise
 payload = proto.read_message(received)
 
 # As of now, the handshake should be finished (as we are using NN pattern). 
 # Any further calls to write_message or read_message would raise NoiseHandshakeError exception.
 # We can use encrypt/decrypt methods of NoiseBuilder now for encryption and decryption of messages.
-encrypted_message = proto.encrypt('This is an example payload')
+encrypted_message = proto.encrypt(b'This is an example payload')
+sock.sendall(encrypted_message)
 
-ciphertext = sock.recv()
+ciphertext = sock.recv(2048)
 plaintext = proto.decrypt(ciphertext)
+print(plaintext)
+```
+
+The example above covers the connection from the initiator's ("client") point of view. The snippet below is an example of responder's code ("server") using a socket connection to send and receive ciphertext.
+
+```python
+import socket
+from itertools import cycle
+
+from noise.builder import NoiseBuilder
+
+if __name__ == '__main__':
+    s = socket.socket()
+    s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+    s.bind(('localhost', 2000))
+    s.listen(1)
+
+    conn, addr = s.accept()
+    print('Accepted connection from', addr)
+
+    noise = NoiseBuilder.from_name(b'Noise_NN_25519_ChaChaPoly_SHA256')
+    noise.set_as_responder()
+    noise.start_handshake()
+
+    # Perform handshake. Break when finished
+    for action in cycle(['receive', 'send']):
+        if noise.handshake_finished:
+            break
+        elif action == 'send':
+            ciphertext = noise.write_message()
+            conn.sendall(ciphertext)
+        elif action == 'receive':
+            data = conn.recv(2048)
+            plaintext = noise.read_message(data)
+
+    # Endless loop "echoing" received data
+    while True:
+        data = conn.recv(2048)
+        if not data:
+            break
+        received = noise.decrypt(data)
+        conn.sendall(noise.encrypt(received))
 ```
 
 #### Wireguard integration example