Added doc/tex/mod/Pack.

doc/tex/mod/Pack

+@BeginModule
+@Name      = Pack
+@Title     = Pack data
+@Section   = File operations
+@Class     = File operation
+@Arguments = infile outfile
+@Operators = pack
+
+@BeginDescription
+@EndDescription
+@EndModule
+
+
+@BeginOperator_pack
+@Title     = Pack data
+
+@BeginDescription
+Packing reduces the data volume by reducing the precision of the stored numbers.
+It is implemented using the NetCDF attributes @env{add_offset} and @env{scale_factor}.
+The operator @oper{pack} calculates the attributes @env{add_offset} and @env{scale_factor} for all variables.
+The default data type for all variables is automatically changed to 16-bit integer.
+Use the CDO option -b to change the data type to a different integer precision, if needed.
+Missing values are automatically transformed to the current data type.
+@EndDescription
+@EndOperator