Explain the importance of p2p encryption

doc/overview.md

@@ -25,6 +25,14 @@ time a new connection to a peer is created:
   * `TLS_AES_256_GCM_SHA384`
   * `TLS_CHACHA20_POLY1305_SHA256`
 
+Encrypted P2P connections are important because it means passive network spies,
+such as ISPs, cannot tell what nodes are communicating to each other and also
+prevents certain attacks against privacy at the network level, such as looking
+for which node was the first to relay a transaction. Bitcoin has no protection
+against this which is why it's trivial for network spies to tell which node
+(and hence which IP address) created a certain transaction and hence which
+IP address owns which addresses.
+
 ## RPC
 
 Inherited many RPC's from Bitcoin and Zcash with many new ones