DOC / Figure.meca: Use table for supported conventions

[yvonnefroehlich]

Description of proposed changes

Add table for the supported conventions of Figure.meca to docs.

Tabels in RST: https://sublime-and-sphinx-guide.readthedocs.io/en/latest/tables.html

See comment #3517 (comment)

Preview: https://pygmt-dev--3811.org.readthedocs.build/en/3811/api/generated/pygmt.Figure.meca.html#pygmt.Figure.meca

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 command is:

• /format: automatically format and lint the code

[seisman]

Suggested change

	- | moment components
	| in dynes-cm
	- | moment components
	| in :math:`10*{exponent}` dyne-cm

[michaelgrund]

Could also discuss to use only dyn-cm, without the e at the end. I find both versions online but the one without the e is much more prominent.

[yvonnefroehlich]

Jupp! Actually, there are several versions used: "dynes-cm", "dyne-cm", and "dyn-cm" with and without the hyphen 🙃. I prefer “dyn”. Personally, I do not like this hyphen because it's stickly speaking a multiplication between dyn and cm (same as for 10^-7 N m).

[seisman]

Looks good to me.

[seisman]

Perhaps we should add the "skip-changelog" label?