note about compose prefix

p6/README.md

@@ -105,9 +105,14 @@ Note: In both container, you need to set the enviroment variable PROJECT to p6.
 
 ### Cassandra Schema
 
-Inside the `__init__` method, you firstly need to connect to the Cassandra cluster, with `Cluster(['p6-db-1', 'p6-db-2', 'p6-db-3'])`.  You can review how to connect here:
+Inside the `__init__` method, you firstly need to connect to the Cassandra cluster, like in lecture:
 https://git.doit.wisc.edu/cdis/cs/courses/cs544/s25/main/-/tree/main/lec/26-cassandra?ref_type=heads
 
+Note: when running locally, the workers will be named `p6-db-<N>`, but
+the autograder will use a different prefix, `????-db-<N>`.  You can
+use `os.environ['PROJECT']` to get the prefix programmatically and
+connect to the correct Cassandra workers.
+
 Write additional code using the session to run CQL queries to do the following:
 
 * drop a `weather` keyspace if it already exists