behaviour: add simple doc.go (#5055)

## Description

add a simple doc.go to behavior module

Closes: #XXX

behaviour/doc.go

@@ -0,0 +1,42 @@
+/*
+Package Behaviour provides a mechanism for reactors to report behaviour of peers.
+
+Instead of a reactor calling the switch directly it will call the behaviour module which will
+handle the stoping and marking peer as good on behalf of the reactor.
+
+There are four different behaviours a reactor can report.
+
+1. bad message
+
+type badMessage struct {
+	explanation string
+}
+
+This message will request the peer be stopped for an error
+
+2. message out of order
+
+type messageOutOfOrder struct {
+	explanation string
+}
+
+This message will request the peer be stopped for an error
+
+3. consesnsus Vote
+
+type consensusVote struct {
+	explanation string
+}
+
+This message will request the peer be marked as good
+
+4. block part
+
+type blockPart struct {
+	explanation string
+}
+
+This message will request the peer be marked as good
+
+*/
+package behaviour