add Census xD

[afeld]

Your Organization: xD ("experimental data") team at the U.S. Census Bureau
GitHub Organization url: @XDgov
Country/Locality: USA

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.