add note to backend

src/invidious/config.cr

@@ -82,6 +82,8 @@ class Config
 
     @[YAML::Field(converter: Preferences::URIConverter)]
     property public_url : URI = URI.parse("")
+
+    property note : String = ""
   end
 
   # Number of threads to use for crawling videos from channels (for updating subscriptions)