UPGRADING.md in ezmq-0.3.7 vs UPGRADING.md in ezmq-0.4.0

@@ -1,4 +1,13 @@
+Upgrading from 0.3.x to 0.4+
+----------------------------
+
+#listen on EZMQ::Socket and EZMQ::Subscriber now requires a block, previously it was optional.
+
+options[:protocol] has been renamed to options[:transport], to be correct.
+
+options[:transport] is expected to be a :symbol, not a 'string'.
+
 Upgrading from 0.1.x to 0.2+
 ----------------------------
 
 Initializing a socket now allows `protocol`, `address`, and `port` as optional parameters.