Add explicit env to docker compose so that it can hint at usage (#1088)

## Description of changes

*Summarize the changes made by this PR.*
 - Improvements & Bug fixes
- Add explicit env for persist directory defaults to docker compose so
that it can hint at usage
 - New functionality
	 - ...

## Test plan
Existing tests
- [x] Tests pass locally with `pytest` for python, `yarn test` for js

## Documentation Changes
None required

docker-compose.yml

@@ -21,6 +21,7 @@ services:
       - CHROMA_SERVER_AUTH_CREDENTIALS_FILE=${CHROMA_SERVER_AUTH_CREDENTIALS_FILE}
       - CHROMA_SERVER_AUTH_CREDENTIALS=${CHROMA_SERVER_AUTH_CREDENTIALS}
       - CHROMA_SERVER_AUTH_CREDENTIALS_PROVIDER=${CHROMA_SERVER_AUTH_CREDENTIALS_PROVIDER}
+      - PERSIST_DIRECTORY=${PERSIST_DIRECTORY:-/chroma/chroma}
     ports:
       - 8000:8000
     networks:
@@ -28,4 +29,4 @@ services:
 
 volumes:
   backups:
-    driver: local
+    driver: local