Added "Open in Cloud Shell" buttons to README files [(#1254)](GoogleCloudPlatform/python-docs-samples#1254)

Author: michaelawyu

samples/snippets/README.md

@@ -1,5 +1,10 @@
 # Cloud Dataproc API Example
 
+[![Open in Cloud Shell][shell_img]][shell_link]
+
+[shell_img]: http://gstatic.com/cloudssh/images/open-btn.png
+[shell_link]: https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/GoogleCloudPlatform/python-docs-samples&page=editor&open_in_editor=dataproc/README.md
+
 Sample command-line programs for interacting with the Cloud Dataproc API.