Add document links to errors

A link would also be helpful in resolving the error.

link is to:
https://github.com/tj/commander.js#avoiding-option-name-clashes

Author: abetomo

index.js

@@ -468,7 +468,9 @@ class Command extends EventEmitter {
       throw new Error(`option '${option.name()}' clashes with existing property '${option.attributeName()}' on Command
 - call storeOptionsAsProperties(false) to store option values safely,
 - or call storeOptionsAsProperties(true) to suppress this check,
-- or change option name`);
+- or change option name
+
+Read more on https://git.io/JJc0W`);
     }
   };