fix typos in README.md
Merge pull request #51 from nikai3d/patch-1

fix typos in README.md
`(npm|bower) install imager` -> `(npm|bower) install imager-js`
`(npm|bower) install imager` -> `(npm|bower) install imager.js`
Merge pull request #50 from oncletom/fix-packaging-name

[READY] `imager` already taken in npm registry