Document adding extra tasks (ex: spec task)

Author: bootstraponline

README.md

@@ -17,6 +17,18 @@ Appium::Thor::Config.set do
     run 'docs/helpers_docs.md', globs('/lib/appium_thor/helpers.rb')
   end
 end
+
+# Must use '::' otherwise Default will point to Thor::Sandbox::Default
+# Debug by calling Thor::Base.subclass_files via Pry
+#
+# https://github.com/erikhuda/thor/issues/484
+#
+class ::Default < Thor
+  desc 'spec', 'Run RSpec tests'
+  def spec
+    exec 'rspec spec'
+  end
+end
 ```
 
 # Defaults