OSS doc (#462)

Summary:
Pull Request resolved: #462

This diff is a preparation for bundled program documentation, including:
1. move bundled program documentation from tutorial/ to sdk/
2. remove the bento notebook, make its content directly in the .md file
3. elementary update to in line with new api

Differential Revision: D49550056

fbshipit-source-id: a027ca2b5b54c7a6ed2d5136f99d11edc823f414

Author: Gasoonjia