Update README.md

Author: tannerlinsley

README.md

@@ -204,6 +204,8 @@ This library is being built and maintained by me, @tannerlinsley and I am always
 
 # Documentation
 
+> NOTE: These docs are written for the latest version of React Query. If you are looking for a previous version, please use the branch switcher to pick your version and view the old documentation.
+
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