Update README.md about the repositories managed by Pulsar PMC (#6722)
Update README.md about the repositories managed by Pulsar PMC (#6722)

*Motivation*

Currently we manage multiple different repositories for different components and clients.
We should update README to reflect the current state.
yahoo/pulsar,massakam/pulsar,massakam/pulsar,merlimat/pulsar,merlimat/pulsar,massakam/pulsar,merlimat/pulsar,merlimat/pulsar,yahoo/pulsar,yahoo/pulsar,massakam/pulsar,yahoo/pulsar,yahoo/pulsar,yahoo/pulsar,merlimat/pulsar,massakam/pulsar,merlimat/pulsar,massakam/pulsar