Fix Plex readme.

Although rendering properly on Github, the line "--device=/dev/dri:/dev/dri" is not valid markdown and is not rendered correctly on the linuxserver.io site: see https://docs.linuxserver.io/images/docker-plex#intel (the formatting is all messed up). 

This fixes the markdown.

readme-vars.yml

@@ -91,7 +91,9 @@ app_setup_block: |
   
   Hardware acceleration users for Intel Quicksync will need to mount their /dev/dri video device inside of the container by passing the following command when running or creating the container:
 
-  ```--device=/dev/dri:/dev/dri```
+  ```
+  --device=/dev/dri:/dev/dri
+  ```
 
   We will automatically ensure the abc user inside of the container has the proper permissions to access this device.