readme: add region tags (#3421)
readme: add region tags (#3421)

Adding region tags to include in Java Cloud Client Library docs on cloud.google.com
vam-google/google-cloud-java,vam-google/google-cloud-java,vam-google/google-cloud-java,vam-google/google-cloud-java,vam-google/google-cloud-java,vam-google/google-cloud-java