Update release notes with version 0.5.9 info
# Release Notes
+## Changes in Splinter 0.5.9
+
+### Highlights
+
+* The splinter CLI subcommands `splinter authid`, `splinter role`, `splinter
+ permissions`, and `splinter remove-proposal` have been stabilized.
+
+### libsplinter
+
+* Add native protocol structs for `NetworkMessages`. This reduces the need to
+ use protobuf structs directly.
+
+* Updated sawtooth-sabre to fix a memory leak.
+
+### splinter CLI
+
+* Stabilize the feature "permissions" by removing it. This makes the subcommand
+ `splinter permission list` available in the default stable builds.
+
+* Stabilize the feature "authorization-handler-rbac". This makes the Role-based
+ Access Control subcommands `splinter role` and `splinter authid` available in
+ stable builds.
+
+* Stabilize the features "proposal-removal". This makes the subcommand `splinter
+ remove-proposal` available in the default builds.
+
+### splinterd
+
+* Update example config files with new configuration options and documentation.
+
## Changes in Splinter 0.5.8
### Highlights
