Update DOI and version number for v0.6.0

[michaelgrund]

Description of proposed changes

Patches #1808

Relates to #1801

Reminders

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst.
• Write detailed docstrings for all functions/methods.
• If wrapping a new module, open a 'Wrap new GMT module' issue and submit reasonably-sized PRs.
• If adding new functionality, add an example to docstrings or tutorials.

Slash Commands

You can write slash commands (/command) in the first line of a comment to perform
specific operations. Supported slash commands are:

• /format: automatically format and lint the code
• /test-gmt-dev: run full tests on the latest GMT development version

[maxrjones]

Thanks, can you update CITATION.cff as well?

[michaelgrund]

Thanks, can you update CITATION.cff as well?

Done!

[maxrjones]

Thank you!

[weiji14]

Good catch, thanks @michaelgrund! And sorry @meghanrjones for not catching it earlier, I wasn't looking closely enough.

I might need to get some proper glasses, considering that this isn't the first time it's happened (see #1597) 🙂

[maxrjones]

I was looking more at the maintenance release checklist rather than the issue template, and this was the sentence that got me:

Refresh citation information. Specifically, the BibTeX in README.rst and CITATION.cff needs to be updated with any metadata changes. Please follow guidelines in AUTHORSHIP.md for updating the author list in the BibTeX. More information about the CITATION.cff specification can be found at https://github.com/citation-file-format/citation-file-format/blob/main/schema-guide.md

We might as well make this more specific in that 'metadata' changes includes the date and DOI in addition to the authorship list.