docs: describe DJANGO_DB_DIR env var

remove reference to a Docker env var that is no longer used

Author: thekaveman

docs/configuration/environment-variables.md

@@ -6,20 +6,6 @@ The sections below outline in more detail the application environment variables
 
 See other topic pages in this section for more specific environment variable configurations.
 
-## Docker
-
-### `COMPOSE_PROJECT_NAME`
-
-!!! info "Local configuration"
-
-    This setting only affects the app running on localhost
-
-!!! tldr "Docker docs"
-
-    Read more at <https://docs.docker.com/compose/reference/envvars/#compose_project_name>
-
-Name that Docker Compose prefixes to the project for container runs.
-
 ## Amplitude
 
 !!! tldr "Amplitude API docs"
@@ -57,6 +43,17 @@ Boolean:
 
 A list of strings representing the host/domain names that this Django site can serve.
 
+### `DJANGO_DB_DIR`
+
+!!! warning "Deployment configuration"
+
+    You may change this setting when deploying the app to a non-localhost domain
+
+The directory where Django creates its Sqlite database file. _Must exist and be
+writable by the Django process._
+
+By default, the base project directory (i.e. the root of the repository).
+
 ### `DJANGO_DEBUG`
 
 !!! warning "Deployment configuration"