Microsoft Cognitive Services Speech SDK Samples

Added the pronunciation.txt sample file for en-US language (#488)

* Added sample data for custom speech.

* Added the readme for sample data

* Updated the git attribute files

* Added spaces for related text file

* Removed the additional space

* Added the link from home readme to sample data custome speech readme

* Updated the related text to make the sample data better for training.

* Add the pronunciation.txt file for en-US