Add Ravi Pokala (rpokala) to src-committers list.

[rpokala]

Summary

Add myself (rpokala) and my mentor (jhb)

Test Plan

`dot -T pdf -O committers-src.dot'

Confirm that the rpokala node is a new child of the jhb node.

[jhb]

Can't recall how explicit the Committer's Guide is on the commit annotations, but for ones I approve as a mentor you should use 'Approved by: jhb (mentor)'. You don't need to list me as a reviewer in addition to an approver.