Revise recommended experiment directory structure

[tnixa]

The README has a recommended directory structure for running experiments with multiple models. After trying this for awhile I think it works better to have all the audio files and reference files in a directory outside of the git project or we could create an experiments directory and git ignore it?

[andrewrfreed]

We already had experiments_* in .gitignore so I am inclined to use the experiments subdirectory and add a line to the gitignore. Then the tool works as expected no matter which option you use.