Task: update examples notebook

[mwtoews]

The Jupyter notebook examples are a bit old, and could use a refresh.

For instance reading_netCDF.ipynb has an outdated URL, which should be updated from:

URL = 'http://thredds.ucar.edu/thredds/dodsC/grib/NCEP/GFS/Global_0p5deg/GFS_Global_0p5deg_%04i%02i%02i_%02i%02i.grib2/GC'

to something like

URL = 'https://thredds.ucar.edu/thredds/catalog/grib/NCEP/GFS/Global_0p5deg/GFS_Global_0p5deg_%04i%02i%02i_%02i%02i.grib2/GC'

except there is a "HTTP Status 404" with the "/GC" part. I'm not sure the correct address, but clearly it's changed. Start here for the current address.

---

writing_netCDF.ipynb works nicely, so the steps are:

1. jupyter notebook writing_netCDF.ipynb
2. Cell > Run All
3. Save and Checkpoint

There are possibly other improvements to make, which is why I'm holding back.

[jswhit]

pull request would be welcomed