add 0.6.0 changelog

Author: a3s7p

changelogs/0.6.0.md

@@ -0,0 +1,16 @@
+# 0.6.0
+
+- Depends on `wireleap/common` v0.3.3.
+- Network usage limiting feature added.
+- Added `network_usage` config section and per-contract
+  `network_usage_limit` field.
+- Relay will now disenroll from a contract when the network usage for
+  that contract exceeds the defined value or disenroll from all
+  contracts when the global value is reached.
+
+- Uses interfaces:
+
+  - `clientrelay` v0.2.0
+  - `relaycontract` v0.1.0
+  - `relayrelay` v0.2.0
+  - `relaydir` v0.2.0