[ADAM-1643] Add S3 access documentation.
[ADAM-1643] Add S3 access documentation.

Resolves #1643.

heuermh/adam,bigdatagenomics/adam,heuermh/adam,bigdatagenomics/adam,heuermh/adam,bigdatagenomics/adam,heuermh/adam,bigdatagenomics/adam