Update README.md

priv/server/README.md

@@ -9,7 +9,7 @@ This information is for internal use, ignore this directory if you are not an of
 
 When you are developing the backend for this client you can use this directory to place the self-signed CA certificate you are using for your backend instance.
 
-The filename of the certificate must match the domain name you are using in the `domain` setting.
+The filename of the certificate must match the domain name you are using in the `domain` setting, followed by the `".pem"` termination.
 
 To create the backend server chain for development, look into the private internal documentation.