Document Serilog per-source level

src/Umbraco.Web.UI/config/serilog.Release.config

@@ -8,6 +8,11 @@
         <!-- VALID Values: Verbose, Debug, Information, Warning, Error, Fatal -->
         <add key="serilog:minimum-level" value="Information" />
 
+        <!-- NOTE: This is how sources can have a different level -->
+        <!--
+        <add key="serilog:minimum-level:override:Umbraco.Core.Composing.TypeLoader" value="Warning" />
+        -->
+
         <!-- NOTE: Only one logger below can be enabled, you cannot log JSON & TXT files at the same time -->
 
         <!-- Default JSON log file -->