Documentation updates needed to clarify open() behavior and concept-id usage

[asteiker]

This feedback came from @trevorlang :

1. I think it would be nice to explicitly state that .open() will automatically select based on the environment the code is executing in here. It kind of says it, just not as explicitly as I would like to feel confident. In addition, it might be useful to document somewhere how it is picking which links to use and what happens if s3 links dont exist. Not sure if it states it somewhere else that I just missed. I wouldve liked to had seen it in the API docs for .open() though.

2. concept_id was not mentioned as a parameter for .search_data here and it just happened to work when I tried. Unless that was on purpose and I should avoid using the granule concept id.