Improve the output of RailsInspect::Cli

Give the developer some direction on how to resolve the error so they don't need to read the code to figure it out.

tools/rail_inspector/lib/rail_inspector/cli.rb

@@ -25,7 +25,7 @@ def configuration(rails_path)
       checker = Configuring.new(rails_path)
       checker.check
 
-      puts checker.errors unless checker.errors.empty?
+      puts checker.error_message if checker.errors.any?
       exit checker.errors.empty? unless options[:autocorrect]
 
       checker.write!

tools/rail_inspector/lib/rail_inspector/configuring.rb

@@ -83,6 +83,14 @@ def write!
       File.write(doc_path, doc.to_s)
     end
 
+    def error_message
+      return unless errors.any?
+
+      errors.join("\n") + "\n" +
+        "Make sure new configurations are added to configuring.md#rails-general-configuration in alphabetical order.\n" +
+        "Errors may be autocorrectable with the --autocorrect flag"
+    end
+
     private
       def doc_path
         @rails_path.join(DOC_PATH)