Add Defaulting To Frozen String Literals as a ruby til

ruby/defaulting-to-frozen-string-literals.md

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+# Defaulting To Frozen String Literals
+
+> The cold never bothered me anyway.
+
+The release of Ruby 2.2 introduced the ability to freeze string literals,
+making them immutable. With the release of Ruby 2.3, strings can be frozen
+by default without the use of `#freeze`. By adding the following magic
+comment at the top of a file
+
+```ruby
+# frozen_string_literal: true
+```
+
+all string literals will default to frozen. That means that all string
+literals in that file are immutable, cannot be modified. This gives the Ruby
+interpreter some performance gains due to reduced object allocation.
+
+This is the [issue](https://bugs.ruby-lang.org/issues/11473) that introduced
+it.