Expand Sphinx Dependencies for Documentation Generation

[Kureii]

While following the instructions to generate the Tiled documentation, I encountered missing dependencies on my system. To resolve this, I have added the following packages to the setup instructions:

• myst_parser
• sphinx_design
• sphinx_reredirects

These additions ensure that all necessary components are available for successful documentation generation, aligning the setup with the current requirements.

Changes: Updated dependencies list for Sphinx documentation in the setup instructions. This update should help others avoid missing dependency issues when building the documentation.

[bjorn]

Thanks! Actually, I think it would be better to update this documentation to use the docs/requirements.txt file that was added at some point. Could you adjust the patch accordingly?

[Kureii]

okay, I'll do it.

[bjorn]

Thanks! That seems quite verbose, but I guess the note about using virtual environments could be useful (I should probably be using that myself as well, heh).