Nominate Tong Li as maintainer

Tong Li <litong01@us.ibm.com> has been contributing to Hyperledger
Cello for several months, in terms of code, answering questions and
reviewing pathsets.

Would like to nominate him as new maintainer.

Change-Id: Id31f6678c3fa32736d2e935eaaf9aa48ce5f4c19
Signed-off-by: Baohua Yang <yangbaohua@gmail.com>

MAINTAINERS.md

@@ -4,5 +4,6 @@
 |---|---|---|---|---|
 | Baohua Yang | baohua | yeasy | baohua | yangbaohua@gmail.com |
 | Haitao Yue | hightall | hightall | hightall | hightallyht@gmail.com |
+| Tong Li | tongli | tongli | tongli | litong01@us.ibm.com |
 
 <a rel="license" href="http://creativecommons.org/licenses/by/4.0/"><img alt="Creative Commons License" style="border-width:0" src="https://i.creativecommons.org/l/by/4.0/88x31.png" /></a><br />This work is licensed under a <a rel="license" href="http://creativecommons.org/licenses/by/4.0/">Creative Commons Attribution 4.0 International License</a>.