Add separate licensing page for COVIDcast data

Author: krivard

docs/api/covidcast_licensing.md

@@ -0,0 +1,56 @@
+---
+title: COVIDcast Data Licensing
+parent: COVIDcast Epidata API
+nav_order: 2
+---
+
+# Licensing for Delphi's COVID-19 Data Streams
+
+## Novel Data
+
+These data streams include data produced novelly by Delphi and intentionally and
+openly surfaced by Delphi through this API.
+
+### Creative Commons: Attribution
+
+This data is provided under the terms of the [Creative Commons Attribution
+license](https://creativecommons.org/licenses/by/4.0/). If you use this data,
+you must cite [Delphi's COVIDcast Epidata API](README.md#citing).
+
+COVIDcast signals included:
+
+* `doctor-visits`
+* `hospital-admissions`
+* `indicator-combination`:`nmf_*`
+* `quidel`
+* `fb-survey`
+
+### Creative Commons: Attribution-NonCommercial
+
+This data is provided under the terms of the [Creative Commons
+Attribution-NonCommercial
+license](https://creativecommons.org/licenses/by-nc/4.0/). If you use this data,
+you must cite [Delphi's COVIDcast Epidata API](README.md#citing). You
+may not use this data for commercial purposes.
+
+COVIDcast signals included:
+
+* `chng`
+
+## Republished Data
+
+These data streams are essentially mirrors of their respective sources, and are
+published here subject to the original license provided by the source. More
+information on the license for each source is available on their respective
+pages.
+
+If you use the Delphi's COVIDcast Epidata API to access this data, we
+additionally request you [acknowledge us](README.md#citing) in your product or
+publication.
+
+COVIDcast signals included:
+
+* `ght`
+* `jhu-csse`
+* `safegraph`
+* `usa-facts`