Fix to address Facter ticket: https://tickets.puppetlabs.com/browse/D…

…OCUMENT-890

source/facter/3.11/custom_facts.md

@@ -254,12 +254,15 @@ Facter.add(:sleep) do
       Facter::Core::Execution.execute('sleep 10', options = {:timeout => 5})
       'did not timeout!'
     rescue Facter::Core::Execution::ExecutionFailure
-      'timeout!'
+      Facter.warn("Sleep fact timed out!")
     end
   end
 end
+
 ```
 
+When Facter runs as standalone, using `Facter.warn` ensures that the message is printed to `STDERR`. When Facter is called as part of a catalog application, using `Facter.warn` prints the message to Puppet's log. If an exception is not caught, Facter automatically logs it as an error.
+
 ## Structured facts
 
 Structured facts take the form of either a hash or an array. To create a structured fact, return a hash or an array from the `setcode` statement.