docs: update description

Co-authored-by: Harsh <149176984+hrshya@users.noreply.github.com>
Signed-off-by: Philipp Burckhardt <pburckhardt@outlook.com>

Author: Planeshifter

lib/node_modules/@stdlib/stats/incr/nanmmse/README.md

@@ -53,7 +53,7 @@ var incrnanmmse = require( '@stdlib/stats/incr/nanmmse' );
 
 #### incrnanmmse( window )
 
-Returns an accumulator `function` which incrementally computes a moving [mean squared error][mean-squared-error]. The `window` parameter defines the number of values over which to compute the moving [mean squared error][mean-squared-error].
+Returns an accumulator `function` which incrementally computes a moving [mean squared error][mean-squared-error]. The `window` parameter defines the number of values over which to compute the moving [mean squared error][mean-squared-error], ignoring `NaN` values.
 
 ```javascript
 var accumulator = incrnanmmse( 3 );