message: PSv2: Make it explicitly in the docstring that "chief", "worker", and "ps" task type naming should be used.
  Context: We've received user reporting that having other names for worker/ps hangs at connecting, so I think it'd be helpful to make this part explicit.
diff: @@ -182,11 +182,18 @@ class ParameterServerStrategyV2(distribute_lib.Strategy):
  If `TF_CONFIG` environment variable is set, a
  `tf.distribute.cluster_resolver.TFConfigClusterResolver` should be used as
  - well. Note that for legacy reason, on some platform, "chief" is used as the
  - task type for the coordinator, as the following example demonstrates. Here we
  - set `TF_CONFIG` for the task designated as a parameter server (task type "ps")
  - and index 1 (the second task), in a cluster with 1 chief, 2 parameter servers,
  - and 3 workers. Note that the it needs to be set before the use of
  + well.
  +
  + Since there are assumptions in
  + `tf.distribute.experimental.ParameterServerStrategy` around the naming of the
  + task types, "chief", "ps", and "worker" should be used in the
  + `tf.distribute.cluster_resolver.ClusterResolver` to refer to the coordinator,
  + parameter servers, and workers, respectively.
  +
  + The following example demonstrates setting `TF_CONFIG` for the task designated
  + as a parameter server (task type "ps") and index 1 (the second task), in a
  + cluster with 1 chief, 2 parameter servers, and 3 workers. Note that it needs
  + to be set before the use of
  `tf.distribute.cluster_resolver.TFConfigClusterResolver`.
  Example code for cluster setup:
  