clarify unsafe-get docstring

Author: swannodette

src/main/clojure/cljs/core.cljc

@@ -994,8 +994,9 @@
      `(~'js* ~(core/str "(~{}[~{}][~{}]" astr " = ~{})") ~a ~idx ~idx2 ~@idxv))))
 
 (core/defmacro unsafe-get
-  "Efficient alternative to goog.object/get which lacks opt_val and emits
-  unchecked property access."
+  "INTERNAL. Compiles to JavScript property access using bracket notation. Does
+  not distinguish between object and array types and not subject to compiler
+  static analysis."
   [obj key]
   (core/list 'js* "(~{}[~{}])" obj key))