Add changelog URL to package metadata

[intgr]

When Renovate bot creates an automated pull request to update supervisord, it can automatically include the link to changelog so it's easier to find out what changed.

The URL name has to be one of: 'changelog', 'change log', 'changes', 'release notes', 'news', "what's new" (case insensitive). Source: https://github.com/renovatebot/renovate/blob/c3a87b687ed44a1a100e0e4f91b81e22b7c32482/lib/modules/datasource/pypi/index.ts#L130-L140

[mnaberez]

When Renovate bot creates an automated pull request to update supervisord, it can automatically include the link to changelog so it's easier to find out what changed.

Please do not use bots or submit automated pull requests to this project.

[intgr]

No, you misunderstood.

This PR was not opened using a bot. This PR was created manually.

The reason for submitting this PR is that I am using Renovate bot in a 3rd project, where I also use supervisord. Whenever there is an update, Renovate can directly link to supervisord's changelog, so I don't have to manually search the web to figure out what changed between the versions.

[mnaberez]

Supervisor publishes the changelog at these places:

• Directly on the PyPI release page (https://pypi.org/project/supervisor/)
• In a CHANGES.rst file in the root of the repository (https://github.com/Supervisor/supervisor)
• Linked from the sidebar on the first page of website (http://supervisord.org)

The changelog is also the first hit for "supervisor changelog" on google, bing, and duckduckgo.

I don't think the changelog is difficult to find, so I'd rather not modify setup.py to support this bot. Everything we add to setup.py increases maintenance burden and the possibility that install fails for some reason. I'd prefer to keep setup.py reduced to only what is absolutely necessary for installation.

[mnaberez]

Unrelated to any third party bots, PyPI also displays project_urls under "Project Links" in the sidebar, which may be helpful to users. I'll merge this so the link is shown on PyPI.

[intgr]

Thanks 👍