[DOC] mention latex requirement for building docs in "Contributing" page

[psadil]

Is there an existing issue for this?

• I have searched the existing issues

Describe your proposed suggestion in detail.

The Maintenance page points to a few latex requirements (https://nilearn.github.io/dev/maintenance.html#build-and-deploy-the-documentation), but not the Contributing page. That can be fine, but it led to an error that confused me while trying to build the docs via html-noplot. Specifically, that command uses the flag -W which turns warnings into errors. Without latex, I get this warning (which breaks html-noplot)

WARNING: LaTeX command 'latex' cannot be run (needed for math display), check the imgmath_latex setting

List any pages that would be impacted.

Contributing, section Build and deploy the documentation (https://github.com/nilearn/nilearn/blob/main/CONTRIBUTING.rst)

[ymzayek]

Since adding warnings-as-failures on the partial build, make html-noplot will fail without the latex dependencies but this is not related to adding new code. One suggestion in order not to add a dependency for contributors we could make a separate partial build command that is used in the CI where the dependencies will be installed and revert make html-noplot to old behavior. The other option is to find the right latex distributions to add to our doc requirements in pyproject.toml so that they are easily installed by an environment manager. Either way would avoid pointing contributors to the maintenance docs.

[bthirion]

I think I prefer the first option (dedicated CI). To be discussed.