copy handshake readme into a doc.go for pretty godoc results

net/handshake/doc.go

+/*
+package handshake implements the ipfs handshake protocol
+
+IPFS Handshake
+
+The IPFS Protocol Handshake is divided into three sequential steps
+
+1. Version Handshake (`Hanshake1`)
+
+2. Secure Channel (`NewSecureConn`)
+
+3. Services (`Handshake3`)
+
+Currently these parts currently happen sequentially (costing an awful 5 RTT),
+but can be optimized to 2 RTT.
+
+Version Handshake
+
+The Version Handshake ensures that nodes speaking to each other can interoperate.
+They send each other protocol versions and ensure there is a match on the major
+version (semver).
+
+Secure Channel
+
+The second part exchanges keys and establishes a secure comm channel. This
+follows ECDHE TLS, but *isn't* TLS. (why will be written up elsewhere).
+
+Services
+
+The Services portion sends any additional information on nodes needed
+by the nodes, e.g. Listen Address (the received address could be a Dial addr),
+and later on can include Service listing (dht, exchange, ipns, etc).
+*/
+package handshake