Added README for grid_to_ncdf tools

grid_to_ncdf/README_gridncdf.txt

+================================================================
+
+ FLEXINVERT-Plus BINARY TO NETCDF CONVERTOR
+
+================================================================
+
+Description:
+  Converts FLEXPART grid_time files from sparse binary format
+  to netcdf. Note this is not needed to run FLEXINVERT-Plus but
+  is an extra tool that users may find helpful, e.g. for viewing
+  the footprints.
+
+Usage:
+  1) compile with gfortran using: make
+  2) edit the SETTINGS file
+  3) run using e.g. nohup ./grid_to_ncdf > myoutput &
+