Fix: incorrect storage job name format.

docs/storage-transfer.md

@@ -158,6 +158,8 @@ The connected agents of the pool are listed on the Agent pools page of the Googl
 
 Role: **Job creator**
 
+The name of a transfer job with a POSIX filesystem source or destination must start with `OPI`, so `STS_JOB_NAME` in `env.sh` has this prefix.
+
 `test_sts.sh` runs on the admin workstation and performs the following steps:
 
 1. Switches to the `wif-test` gcloud configuration.