Add README.md files for samples

[priyaananthasankar]

Fan In Fan Out Tensorflow - completed
Wait for External Event - pending

These samples need a proper README file.

[davidmrdavid]

These two already have README files, so I'll be closing this.
I do want to improve our sample READMEs in the future, but first there's a bit more dev work to get done, as we prepare towards GA. In the meantime, the current READMEs should do the trick :)