Updated Custom Configuration (markdown)

Custom-Configuration.md

@@ -21,6 +21,7 @@ The configuration file is split into sections:
 * [proxy](#proxy)
 * [authentication](#authentication)
 * [admin](#admin)
+* [error](#error)
 
 _System_: This section specifies system specific parameters
 
@@ -137,4 +138,20 @@ Advertises an email address where people can reach the administrator.
 
 `""`    = Disabled (default)
 
-Example: `email = "admin@instance.rss-bridge.com"`
+Example: `email = "admin@instance.rss-bridge.com"`
+
+## error
+
+This section provides following parameters:
+
+- [output](#output)
+
+### output
+
+Defines how error messages are returned by RSS-Bridge
+
+`feed`: As part of the feed (default)
+
+`http`: As HTTP error message
+
+`none`: No errors are reported