Add contribution documentation

[GilOliveira]

A frequent issue delaying the addition of new icons is the lack of documentation on how to contribute the font files to the source tree from an SVG version of the logos (see #174 (comment), #184 (comment)).

A simple document explaining the steps to generate the font files (such as a CONTRIBUTING file) would streamline the addition of new icons by educating contributors on how to generate the files needed so that they can submit the PR themselves, thus making the process of adding new icons faster, and also allowing the repo maintainers to save the time they would've spent doing it themselves.

[nfrerebeau]

I will try to add a guide to describe the main steps. The main difficulty is the availability of a workable logo, provided by the organization (e.g. #174, I had to contact the arXiv team to ask if they have a monochrome logo as I can't modify it myself).

[GilOliveira]

I will try to add a guide to describe the main steps.

Thank you so much!

The main difficulty is the availability of a workable logo, provided by the organization.

I can tell, but for folks who either already have a workable version of the logo, or are able to do it themselves, I recon it will save you a lot of effort if people were able to submit the PR themselves, rather than submitting the SVG and you having to do the whole font regenerating yourself.