Fix Read the Docs build failure

_build/_sources/patterns/caching.rst.txt

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+Caching
+=======
+
+When your application runs slow, throw some caches in.  Well, at least
+it's the easiest way to speed up things.  What does a cache do?  Say you
+have a function that takes some time to complete but the results would
+still be good enough if they were 5 minutes old.  So then the idea is that
+you actually put the result of that calculation into a cache for some
+time.
+
+Flask itself does not provide caching for you, but `Flask-Caching`_, an
+extension for Flask does. Flask-Caching supports various backends, and it is
+even possible to develop your own caching backend.
+
+
+.. _Flask-Caching: https://flask-caching.readthedocs.io/en/latest/