add content_type option to generic camera (home-assistant#2887)

source/_components/camera.generic.markdown

@@ -35,6 +35,7 @@ Configuration variables:
 - **password** (*Optional*): The password for accessing your camera.
 - **authentication** (*Optional*): Type for authenticating the requests `basic` (default) or `digest`.
 - **limit_refetch_to_url_change** (*Optional*): True/false value (default: false). Limits refetching of the remote image to when the url changes. Only relevant if using a template to fetch the remote image.
+- **content_type** (*Optional*): Set the content type for the IP camera if it is not a jpg file (default: `image/jpeg`). Use `image/svg+xml` to add a dynamic svg file.
 
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