Changelog entry for v0.6.1

[seisman]

Description of proposed changes

This PR adds a changelog entry for v0.6.1.

Preview: https://pygmt-pyr0d849n-gmt.vercel.app/changes.html

Previous release at #1808

Changelog made by following the instructions at https://github.com/GenericMappingTools/pygmt/blob/main/doc/maintenance.md#updating-the-changelog

TODO:

• Copy the draft release note from https://github.com/GenericMappingTools/pygmt/releases to doc/changes.md
• Update the DOI badge
• Update citation information https://github.com/GenericMappingTools/pygmt#citing-pygmt and CITATION.cff
• Add the documentation link https://github.com/GenericMappingTools/pygmt#documentation-for-other-versions
• Add highlights
• Update with any remaining PRs merged before release
• Edit the change list to remove any trivial changes (updates to the README, typo fixes, CI configuration, etc)
• Edit the list of people who contributed to the release, linking to their GitHub account. Sort their names by the number of commits made since the last release (e.g., use git shortlog HEAD...v0.1.2 -sne).

Relates to #1856

[michaelgrund]

Looks good to me!

[weiji14]

Looks good, thanks @seisman! Just need to change the date to Apr 11 and should be good to merge.