html code formatting
fix typos

- YALM -> YAML
- folders * is -> folders * are
changes to storage API introduction

- change heading to 'Overview' to match nav
- add link to google cloud storage
- suggest alternatives upfront for simpler use cases:
  - access files via google API (no authentication)
  - manage storage by logging in to account
- rest of doco is about using storage API to manage files
Merge commit '61a6196c7e3b1a76288e0c96459c913282bcd10e' into HEAD