Add a webhook for readthedocs on Github to continuously deploy the documentation.

[jiqicn]

Check the official docs of RTD for how-to: https://docs.readthedocs.io/en/stable/integrations.html#github.

[jiqicn]

Checked this webpage to setup the webhook: https://docs.readthedocs.io/en/stable/guides/setup/git-repo-manual.html.

Trouble shooting:

• Permission issues: Read the docs should be granted permissions of managing webhooks of the target repos. Problem solved by following the explanation on this link: https://docs.readthedocs.io/en/stable/guides/setup/git-repo-manual.html#webhook-activation-failed-make-sure-you-have-the-necessary-permissions.