DOC: hint to passphrase

README_SETUP.md

@@ -59,6 +59,9 @@ you need to uncomment the respective sections in `envoy.yml` and `docker-compose
 The given configuration assumes, that the certificate files are placed in a folder
 `compose/certs` and named `caosdb.key.pem` and `caosdb.cert.pem`.
 
+It is assumed, that `caosdb.key.pem` does not have a passphrase. You can remove one
+with `openssl rsa -in oldKey.pem -out newKey.key`.
+
 
 ## Configuration
 ### Bind IP