Update changelog for 5.0

Author: brianc

NEWS.md renamed to CHANGELOG.md

@@ -4,6 +4,16 @@ For richer information consult the commit log on github with referenced pull req
 
 We do not include break-fix version release in this file.
 
+### v5.0.0
+
+#### Breaking Changes
+- `require('pg').native` now returns null if the native bindings cannot be found; previously, this threw an exception.
+
+#### New Features
+- better error message when passing `undefined` as a query parameter
+- support for `defaults.connectionString`
+- support for `returnToHead` being passed to [generic pool](https://github.com/coopernurse/node-pool)
+
 ### v4.5.0
 - Add option to parse JS date objects in query parameters as [UTC](https://github.com/brianc/node-postgres/pull/943)