DOC: Improve link to the GMT documentation

[seisman]

Address #3881.

For comparison:

• Old version: https://www.pygmt.org/v0.15.0/api/generated/pygmt.grdfill.html
• New version: https://pygmt-dev--3944.org.readthedocs.build/en/3944/api/generated/pygmt.grdfill.html

Old	New version 1	New version 2

[seisman]

I'll apply the same changes to other wrappers if approved.

[yvonnefroehlich]

For me this change looks good in the docs.

[seisman]

Ping @michaelgrund and @weiji14 for comments before I make changes.

Actually, I'd still like to rephrase the sentence so the links appear on one line, but I haven’t found a good solution yet.

[yvonnefroehlich]

Hm. If it should fit into one line, maye we can put the link to the docs within the grdfill.
Not sure, if the link works in this way or the full URL is required.

Suggested change

	.. note::
	Wraps the GMT module ``grdfill``.
	The GMT documentation is at :gmt-docs:`grdfill.html`.
	.. note::
	Wraps the GMT module [``grdfill``](:gmt-docs:`grdfill.html`).

[seisman]

I'm not sure if your solution works, but the one below is shorter and should work. This way, the URL isn't explicitly shown, so readers might not realize that it links to the GMT documentation. Is it OK?

Suggested change

	.. note::
	Wraps the GMT module ``grdfill``.
	The GMT documentation is at :gmt-docs:`grdfill.html`.
	Wraps the GMT module :gmt-docs:`grdfill <grdfill.html>`.