update Readme

docker/.env.example

@@ -1,4 +1,5 @@
 PORT=3000
+PASSPHRASE=MYPASSPHRASE # Passphrase used to create encryption key
 # FLOWISE_USERNAME=user
 # FLOWISE_PASSWORD=1234
 # DEBUG=true

docker/docker-compose.yml

@@ -6,6 +6,7 @@ services:
         restart: always
         environment:
             - PORT=${PORT}
+            - PASSPHRASE=${PASSPHRASE}
             - FLOWISE_USERNAME=${FLOWISE_USERNAME}
             - FLOWISE_PASSWORD=${FLOWISE_PASSWORD}
             - DATABASE_PATH=${DATABASE_PATH}