Merge branch 'release/2.0.1'
fixed version
Guide users to fix major version, since we're planning to release a backwards-incompatible change

See http://guides.cocoapods.org/syntax/podfile.html#pod
and http://semver.org/
Merge pull request #42 from YUKAI/readme-fix-major-version-number

Guide users to fix major version, since we're planning to release a backwards-incompatible change