[README] Missing link to the API docs

[aprotyas]

There is a broken API docs link in the last paragraph of the package README:

There is a C++ API that can be integrated into your own process, you can find the API docs here.

Can that link now be replaced with this? https://docs.ros.org/en/ros2_packages/rolling/api/domain_bridge/index.html

[jacobperron]

Yes, we can probably point the link to the docs hosted at docs.ros.org.