Add @jack-berg as maintainer (#272)

Author: trask

README.md

@@ -54,6 +54,7 @@ Approvers ([@open-telemetry/java-contrib-approvers](https://github.com/orgs/open
 Maintainers ([@open-telemetry/java-contrib-maintainers](https://github.com/orgs/open-telemetry/teams/java-contrib-maintainers)):
 
 - [Anuraag Agrawal](https://github.com/anuraaga), AWS
+- [Jack Berg](https://github.com/jack-berg), New Relic
 - [Mateusz Rzeszutek](https://github.com/mateuszrzeszutek), Splunk
 - [Nikita Salnikov-Tarnovski](https://github.com/iNikem), Splunk
 - [Ryan Fitzpatrick](https://github.com/rmfitzpatrick), Splunk