docs(norostat): note that updates stopped November 2020

Author: dshemetov

docs/api/norostat.md

@@ -13,6 +13,8 @@ General topics not specific to any particular endpoint are discussed in the
 [contributing](README.md#contributing), [citing](README.md#citing), and
 [data licensing](README.md#data-licensing).
 
+**NOTE**: This data source stopped acquiring data in November 2020.
+
 ## NoroSTAT Data
 
 ... <!-- TODO -->