Update readme.md for tracing (#434)
Update readme.md for tracing (#434)

* Update readme.md for tracing

Updated OpenCensus mentions to OpenTelemetry since this is what we use now for instrumenting the app with traces.

Co-authored-by: Gloria Zhao <4bdc20ee2d652300aeec4111d1af68d999ae1dec@google.com>
GoogleCloudPlatform/cloud-ops-sandbox,GoogleCloudPlatform/cloud-ops-sandbox,GoogleCloudPlatform/cloud-ops-sandbox,GoogleCloudPlatform/cloud-ops-sandbox,GoogleCloudPlatform/cloud-ops-sandbox,GoogleCloudPlatform/cloud-ops-sandbox,GoogleCloudPlatform/cloud-ops-sandbox