Update instructions for checking README syntax for release

[maxrjones]

Description of the desired feature

The instructions from the maintenance guide for checking the README syntax prior to a release are outdated since we no longer use setup.py.

We should be able to use twine to check the long description instead, ideally as part of the CI rather than as a manual part of the release process.

Are you willing to help implement and maintain this feature? Yes

[weiji14]

We should be able to use twine to check the long description instead, ideally as part of the CI rather than as a manual part of the release process.

Sounds good, maybe put the twine check somewhere in https://github.com/GenericMappingTools/pygmt/blob/v0.7.0/.github/workflows/publish-to-pypi.yml following what you did in xarray-contrib/xbatcher#108?

[seisman]

As I understand it, twine check only checks if the long description will render correctly, which may not help if someone mistypes *abc* as **abc*.

Perhaps we can simply visit the TestPyPI release history page (https://test.pypi.org/project/pygmt/#history), and click to the README page of the latest dev release (e.g., https://test.pypi.org/project/pygmt/0.7.1.dev130/ now).

[seisman]

Just found a issue by visiting the latest dev version on the TestPyPI page (https://test.pypi.org/project/pygmt/0.7.1.dev157/).

The maintainer information are not correctly shown:

[maxrjones]

Just found a issue by visiting the latest dev version on the TestPyPI page (https://test.pypi.org/project/pygmt/0.7.1.dev157/).

The maintainer information are not correctly shown

From https://packaging.python.org/en/latest/specifications/core-metadata/#maintainer:

Note that this field is intended for use when a project is being maintained by someone other than the original author: it should be omitted if it is identical to Author.

I see this in many packages, but I think we should not have separate maintainers metadata because it is identical to authors.