MAINT - Add multiple maintainers

[trallard]

To reduce redundancy, it would be best to add more maintainers to:

• the package itself
• PyPI
• conda-forge

[steff456]

I already added @trallard as maintainer in

• [x] the package
• [x] PyPI - https://pypi.org/project/accessible-pygments/
• [x] conda-forge - https://github.com/conda-forge/accessible-pygments-feedstock/pull/2

So I'm closing this issue!