add data files for netCDF_intro exercises
Merge remote-tracking branch 'upstream/master' before adding
netcdf_intro files.
added presentations files for netcdf_intro
tweak netcdf_intro presentation
Merge branch 'master' of https://github.com/russrew/unidata-python-workshop

Conflicts:
	presentations/netcdf-intro.pdf
	presentations/netcdf-intro.pptx
Merge branch 'master' of https://github.com/Unidata/unidata-python-workshop