docs: add note

Signed-off-by: Athan <kgryte@gmail.com>

Author: kgryte

lib/node_modules/@stdlib/stats/base/ndarray/nanmin-by/docs/repl.txt

@@ -16,6 +16,8 @@
     If the callback function does not return any value (or equivalently,
     explicitly returns `undefined`), the value is ignored.
 
+    If the callback function returns `NaN`, the value is ignored.
+
     Parameters
     ----------
     arrays: ArrayLikeObject<ndarray>