Add Mexico/satmx, for Servicio de Administración Tributaria (SAT)

Thanks for the contribution! Below is a template that can make it easier when submitting your Organization:

Your Organization: Servicio de Administración Tributaria (SAT)
GitHub Organization url: @satmx
Country/Locality: Mexico City, Mexico

Inclusion requirements:

• Referenced account is an Organization not a User^
• If this is a government project, your Organization's description should include a reference to your country/agency.
• Make sure your Organization includes at least one public repository
• Please also include a URL for your organization that links back to your organization or agency homepage.

^ If you want to convert your account to an org, details can be found here: https://help.github.com/articles/converting-a-user-into-an-organization/

❤️ GitHub Government Contributors