Actually Add Samples

[catvec]

In the README (and docs.cloud.google.com site) it mentions that you can check out the samples directory. However when you click the link to look in the samples directory it is empty.

It would be helpful to actually add some samples. Or remove that link.

[parthea]

Transferring to google-cloud-python as the code for python-firestore will be migrated there in 1-3 weeks.