POC: WIP: DOC: Add basic tutorial "Plotting single-parameter symbols"

[yvonnefroehlich]

Description of proposed changes

Add a basic tutorial for plotting symbols, explaining the style, size, and symbol parameters.

TODO: Multi parameter symbols ?

Related basic tutorials:

• Plotting lines: https://www.pygmt.org/dev/tutorials/basics/lines.html
• Plotting text: https://www.pygmt.org/dev/tutorials/basics/text.html
• Plotting polygons: WIP: DOC: Add basic tutorial "Plotting polygons" #3593

Fixes #3595

Preview: https://pygmt-dev--3598.org.readthedocs.build/en/3598/tutorials/basics/symbols.html

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.
• Use underscores (not hyphens) in names of Python files and directories.

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specific operations. Supported slash command is:

• /format: automatically format and lint the code

[michaelgrund]

Suggested change

	# points with the same symbol and size. Via the ``fill`` parameter the symbols can be
	# filled with a color or pattern, and ``pen`` can add an outline (pass an argument in
	# points with the same symbol and size. The symbols can be
	# filled with a color or pattern via the ``fill`` parameter, and
	# ``pen`` can add an outline (pass an argument in

[yvonnefroehlich]

@michaelgrund thanks for already looking at this PR. However, to be more precise regarding single- and multi-parameter symbols I made larger changes to documentation and moved this general part on the fill and pen parameter to the introduction at the top.