error-reporting: Address doc inconsistencies (#2247)
error-reporting: Address doc inconsistencies (#2247)

In the README file:

* Removed documentation on automatically handling
  uncaughtExceptions since that logic no longer exists in the
  code.
* Removed the statement saying that this project is not an
  official Google project.
* Added clarity to what configuration is needed in different
  environments.
* Removed an invalid reference to the Stackdriver Trace agent
  for Node.js.
* Did some refactoring to make the documentation easier to read.

* Address GitHub comments

GoogleCloudPlatform/gcloud-node,GoogleCloudPlatform/gcloud-node,googleapis/google-cloud-node,googleapis/google-cloud-node,callmehiphop/gcloud-node,googleapis/google-cloud-node,googleapis/google-cloud-node,jgeewax/gcloud-node,callmehiphop/gcloud-node,jgeewax/gcloud-node,GoogleCloudPlatform/gcloud-node