docs(streaming): make library_path optional in the example config

A webstation container that mounts the library at /romm/library, like RomM,
needs no library_path, so the example comments it out and says when to set
it. The dev compose comment now says why the host-run dev backend still
needs it.

docker-compose.streaming.yml

@@ -23,8 +23,8 @@ services:
     volumes:
       # Emulator configs, BIOS, save data, and the broker's export directory.
       - ./romm_mock/webstation:/config
-      # Activate rejects any rom path outside /romm, and config.yml's
-      # library_path has to name this mount.
+      # Activate rejects any rom path outside /romm. The dev backend runs on
+      # the host, so romm_mock's config.yml sets library_path to this mount.
       - ./romm_mock/library:/romm/library:ro
     ports:
       - "3010:3000" # HTTP, expects a reverse proxy in front

examples/config.example.yml

@@ -225,7 +225,7 @@
 #     - protocol: webstation
 #       host: https://192.168.1.56:3010  # browser-facing UI, must be https
 #       subfolder: /streaming            # matches the container's SUBFOLDER
-#       library_path: /romm              # where it mounts your ROM library
+#       # library_path: /mnt/games/library  # only if the container can't mount the library at /romm/library like RomM does
 #       broker_secret: change-me         # matches the container's BROKER_SECRET
 #       label: Emulation station
 #       broker_host: http://192.168.1.56:3010  # server-to-broker URL, when RomM can't dial `host` itself