Add Gravity files to 00README.txt
Add Gravity files to 00README.txt

Sciumo/GeographicLib,Sciumo/GeographicLib,geographiclib/geographiclib,geographiclib/geographiclib,Sciumo/GeographicLib,Sciumo/GeographicLib,geographiclib/geographiclib,Sciumo/GeographicLib,Sciumo/GeographicLib,geographiclib/geographiclib,Sciumo/GeographicLib,Sciumo/GeographicLib