Added mercantile to requirements and README

README.md

@@ -20,6 +20,7 @@ Dependencies (not all are needed for all individual scripts):
 - json (2.0.9 or later)
 - iso3166 (1.0.1 or later)
 - pyproj (1.9.5.1 or later)
+- mercantile (1.2.1 or later)
 
 # Copyright and Copyleft
 

requirements.txt

@@ -7,3 +7,4 @@ matplotlib >= 2.1.1
 h5py >= 2.7.1
 iso3166 >= 1.0.1
 pyproj >= 1.9.5.1
+mercantile >= 1.2.1
\ No newline at end of file