[broadband][s]: create broadband file and add microsoft dataset on US broadband.

Author: rufuspollock

broadband.md

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+---
+title: Broadband Data
+description: Data on broadband access and usage around the world
+keywords: broadband data
+date: 2021-05-14
+modified: 2021-05-14
+---
+
+* United States Broadband Usage Percentages Dataset
+(published by Microsoft) in 2021 https://github.com/microsoft/USBroadbandUsagePercentages