improve data packet picture

i2p2www/pages/site/docs/transport/ntcp.html

@@ -34,9 +34,17 @@ the NTCP transport sends individual I2NP messages, with a simple checksum.
 The unencrypted message is encoded as follows:
 {%- endtrans %}</p>
 {% highlight lang='dataspec' %}
-+-------+-------+--//--+---//----+-------+-------+-------+-------+
-| sizeof(data)  | data | padding | Adler checksum of sz+data+pad |
-+-------+-------+--//--+---//----+-------+-------+-------+-------+
++-------+-------+-------+-------+-------+-------+-------+-------+
+| sizeof(data)  |                                               |
++-------+-------+                                               +
+|                            data                               |
+~                                                               ~
+|                                                               |
++                                       +-------+-------+-------+
+|                                       |        padding          
++-------+-------+-------+-------+-------+-------+-------+-------+
+                                | Adler checksum of sz+data+pad |
++-------+-------+-------+-------+-------+-------+-------+-------+
 {% endhighlight %}
 <p>{% trans -%}
 The data is then AES/256/CBC encrypted. The session key for the encryption