Update settings description

config/settings/__init__.py

 """
 Django settings for gracedb project.
+Environment variable DJANGO_SETTINGS_MODULE should be set for a
+given instance to determine the settings to run.
 
-Description of settings files:
-    __init__.py   - this file; determines whether to use production or test
-                    settings for this GraceDB instance.
-    local.py      - generated by Puppet, contains paths to useful directories,
-                    virtualenv, and other settings.
-    secret.py     - generated by Puppet, contains secret settings like the
-                    database password, API keys, etc.
-    base.py       - contains the basic settings for running a GraceDB server.
-                    These can be overridden in production.py or dev.py. Uses
-                    settings in local.py and secret.py.
-    production.py - defines settings for a production GraceDB instance. Imports
-                    base.py settings and overrides/adds settings.
-    dev.py        - defines settings for a development or testing server.
-                    Imports base.py settings and overrides/adds settings.
+
+Description of settings:
+    BASE SETTINGS - not to be used as a full settings configuration
+    ---------------------------------------------------------------
+    base.py   - contains the basic settings for running a GraceDB
+                server.
+    secret.py - generated by Puppet, contains secret settings like the
+                database password, API keys, etc. For use with VM-based
+                deployments.  DO NOT EDIT.
+
+    Virtual machine deployments
+    ---------------------------
+    vm/production.py - settings for a VM-based production instance deployed
+                       with Puppet.
+    vm/dev.py        - settings for Va M-based production instance deployed
+                       with Puppet.
+
+    Container-based deployments
+    ---------------------------
+    NOTE: many settings are imported from environment variables for
+    this deployment type!
+
+    container/production.py - settings for a container-based deployment
+                              of a production instance.
+    container/dev.py        - settings for a container-based deployment of a
+                              development instance.
 """