Preliminary outline for reading/writing docs

[alex-s-gardner]

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This is a preliminary edit to update the reading and writing docs.

I'm hoping to get help getting the NCDatasets and HDF5 examples working that are located at the end of the writing.jl file.

[rafaqz]

Dont worry about the tests ucdavis (worldclim) is down, as usual

[rafaqz]

Note we cant write to hdf5 ;)