OpenMM-ML 1.1

This release fixes a bug in creating mixed ML/MM systems, and adds an option to use a single model out of the ensemble of ANI models.

What's Changed

• Added installation instructions to README by @peastman in #49
• Added modelIndex option by @peastman in #51
• Fixed indexing error creating mixed system by @peastman in #56
• Updated version number to 1.1 by @peastman in #58

Full Changelog: 1.0...1.1