Fixes #6024.

Adding documentation for exit codes used by 'gh'

pkg/cmd/root/help_topic.go

@@ -138,6 +138,10 @@ var HelpTopics = map[string]map[string]string{
 			
 			- If a command fails for any reason, the exit code will be 1
 
+			- If a command is running but gets cancelled, the exit code will be 2
+
+			- If a command encounters an authentication issue, the exit code will be 4
+
 			NOTE: It is possible that a particular command may have more exit codes, so it is a good 
 			practice to check documentation for the command if you are relying on exit codes to 
 			control some behavior.