Create README.md

READ_GRIB reads WMO international exchange GRiB formatted data files into MATLAB. It has various input modes, including extraction of individual GRiB records by record number, extraction by parameter name (which is not unique), and generating an inventory of the GRiB file contents. It has been tested on the following standard model output files: AVN, ETA, RUC, ECMWF, and WAM. The default GRiB parameter table used is the NCEP Operational table.

Current Version = r4 

Calls to READ_GRIB now look like:
  >> grib_struct=read_grib(gribname,irec,'HeaderFlag',0,'ParamTable','ECMWF128');