Update README.md

Merge pull request fschultz#11 from fschultz/experimental

Release 3.0
- Added multi-threaded optimized image filters
- Added support for saving image dimensions

Merge pull request fschultz#10 from fschultz/dpi-fix

Version 2.0.6

Merge pull request fschultz#6 from fschultz/release-2-0-5

Release 2.0.5