docs: fix notes

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

Author: kgryte

lib/node_modules/@stdlib/stats/base/ndarray/snanmeanwd/README.md

@@ -78,8 +78,7 @@ The function has the following parameters:
 
 ## Notes
 
--   If `N <= 0`, both functions return `NaN`.
--   If every indexed element is `NaN`, both functions return `NaN`.
+-   If provided an empty one-dimensional ndarray, the function returns `NaN`.
 
 </section>