Description of proposed changes

Since Sphinx-Gallery 0.17.0, building the Documentation fails (see #3346 (comment)). It seems like the problem is the pygmt/examples/projections/table folder which only contains the README file with the projection table (see #3346 (comment)). To fix this and get rid of the table folder, this PR moves the projection table to the "Technical References".

Fixes #3346

Previews

• https://pygmt-dev--3356.org.readthedocs.build/en/3356/projections/index.html
• https://pygmt-dev--3356.org.readthedocs.build/en/3356/techref/
• https://pygmt-dev--3356.org.readthedocs.build/en/3356/techref/projection_table.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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