Change some "help" documentation.

I added a few comment lines and tested a few of the "help <commandname>" examples.

Do these methods from "help ncvariable.data" work?
 
  d = ds.data(variableName, first)
  d = ds.data(variableName, first, last)
  d = ds.data(variableName, first, last, stride)

I can do:

    ds = cfdataset('http://dods.mbari.org/cgi-bin/nph-nc/data/ssdsdata/deployments/m1/200810/OS_M1_20081008_TS.nc');
    v = ds.variable('TEMP');
    %    t = v.data([1 1 1 1], [10 2 1 1]);  % seems to fail
    t=v.data(1:10,1:2,1,1);   % seems to work