Update readthedocs.org so it builds again

[drewnoakes]

We use https://app.readthedocs.org/projects/netmq/ to build the documentation site hosted at https://netmq.readthedocs.io/en/latest/

Several years ago It stopped updating in response to changes here on the site. We probably just need a webhook in the config.

I don't have permissions on readthedocs.org for the NetMQ project. The current maintainers are @somdoron and @sachabarber.

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@somdoron or @sachabarber, could you please add me as an admin on that site so I can get it working again. Should only take a minute. Thanks.