Add lzchen to maintainers (open-telemetry#784)

* Add lzchen to maintainers

Closes open-telemetry#778.

Co-authored-by: alrex <aboten@lightstep.com>

Author: toumorokoshi

README.md

@@ -107,7 +107,6 @@ Approvers ([@open-telemetry/python-approvers](https://github.com/orgs/open-telem
 - [Chris Kleinknecht](https://github.com/c24t), Google
 - [Diego Hurtado](https://github.com/ocelotl)
 - [Hector Hernandez](https://github.com/hectorhdzg), Microsoft
-- [Leighton Chen](https://github.com/lzchen), Microsoft
 - [Mauricio Vásquez](https://github.com/mauriciovasquezbernal), Kinvolk
 - [Reiley Yang](https://github.com/reyang), Microsoft
 
@@ -116,16 +115,17 @@ Approvers ([@open-telemetry/python-approvers](https://github.com/orgs/open-telem
 Maintainers ([@open-telemetry/python-maintainers](https://github.com/orgs/open-telemetry/teams/python-maintainers)):
 
 - [Alex Boten](https://github.com/codeboten), LightStep
+- [Leighton Chen](https://github.com/lzchen), Microsoft
 - [Yusuke Tsutsumi](https://github.com/toumorokoshi), Zillow Group
 
+*Find more about the maintainer role in [community repository](https://github.com/open-telemetry/community/blob/master/community-membership.md#maintainer).*
+
 ### Thanks to all the people who already contributed!
 
 <a href="https://github.com/open-telemetry/opentelemetry-python/graphs/contributors">
   <img src="https://contributors-img.web.app/image?repo=open-telemetry/opentelemetry-python" />
 </a>
 
-*Find more about the maintainer role in [community repository](https://github.com/open-telemetry/community/blob/master/community-membership.md#maintainer).*
-
 ## Release Schedule
 
 OpenTelemetry Python is under active development.