chore: add a Code of Conduct (#350)
chore: add a Code of Conduct (#350)

Co-authored-by: google-cloud-policy-bot[bot] <92a6cf9f50641a93109ccdcf7086298233589fca@users.noreply.github.com>
Co-authored-by: kolea2 <0af1f43147f9dfd96b99d84e9c1903f5f57dddf9@users.noreply.github.com>
GoogleCloudPlatform/cloud-bigtable-examples,GoogleCloudPlatform/cloud-bigtable-examples,GoogleCloudPlatform/cloud-bigtable-examples,GoogleCloudPlatform/cloud-bigtable-examples