README.release

* create a release branch ('vX.Y.Zrel').  In the release branch...
* make sure version number in PKG-INFO, setup.py and netCDF4/_netCDF4.pyx are up to date
  (in _netCDF4.pyx, change 'Version' in first line of docstring at top of file,
   and __version__ variable).
* update Changelog and README.md as needed. 
* commit and push all of the above changes.
* install the module (python setup.py install), then run 'sh create_docs.sh'
  to update html docs.  Commit and push the update to docs/netCDF4/index.html.
* create a pull request for the release branch.
* After release branch has been merged, tag a release
   git tag -a vX.Y.Zrel -m "version X.Y.Z release"
   git push origin --tags
* push an empty commit to the netcdf4-python-wheels repo to trigger new builds.
  (e.g. git commit --allow-empty -m "Trigger build")
  You will likely want to edit the .travis.yml file at 
  https://github.com/MacPython/netcdf4-python-wheels to specify the BUILD_COMMIT before triggering a build.
* update the pypi entry, upload the wheels from wheels.scipy.org.
  Lastly, create a source tarball using
  'python setup.py sdist' and upload to pypi.
* update web docs by copying docs/netCDF4/index.html somewhere, switch
  to the gh-pages branch, copy the index.html file back, commit and push
  the updated index.html file (see README.gh-pages).