docs: add note

Author: kgryte

lib/node_modules/@stdlib/ndarray/map/README.md

@@ -155,6 +155,8 @@ The callback function is provided the following arguments:
     // returns <ndarray>
     ```
 
+-   The function **always** returns an [ndarray][@stdlib/ndarray/ctor] having the same shape and [order][@stdlib/ndarray/orders] as the input [ndarray][@stdlib/ndarray/ctor].
+
 -   For very high-dimensional ndarrays which are non-contiguous, one should consider copying the underlying data to contiguous memory before applying a callback function in order to achieve better performance.
 
 </section>
@@ -206,6 +208,8 @@ console.log( ndarray2array( y ) );
 
 [@stdlib/ndarray/dtypes]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/ndarray/dtypes
 
+[@stdlib/ndarray/orders]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/ndarray/orders
+
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