Adding IAM User Policy documentation to Readme.

This is added to resolve #197
Merge branch 'master' of https://github.com/Breefield/asset_sync into Breefield-master

* 'master' of https://github.com/Breefield/asset_sync:
  Adding IAM User Policy documentation to Readme.
Move IAM policy docs to after asset_sync configuration
Merge branch 'Breefield-master'

* Breefield-master:
  Move IAM policy docs to after asset_sync configuration
  Adding IAM User Policy documentation to Readme.