Add Demodulize A Class Name as a rails til

rails/demodulize-a-class-name.md

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+# Demodulize A Class Name
+
+If you call `.class.name` on an instance of some class, the fully qualified
+name will be returned, module names and all. Consider the following example
+class:
+
+```ruby
+module One
+  module Two
+    class Three
+      ...
+    end
+  end
+end
+```
+
+```ruby
+> One::Two::Three.new.class.name
+#=> "One::Two::Three"
+```
+
+If you just want the unqualified class name; modules not included, you can
+use the `#demodulize` method provided by `ActiveSupport`.
+
+```ruby
+> One::Two::Three.new.class.name.demodulize
+#=> "Three"
+```