docs: describe the updated algorithm

Author: mvasin

README.md

@@ -61,7 +61,7 @@ const MyHalfHeightExampleComponent = ({ children }) => {
 
 Under the hood `use100vh` uses `measureHeight` function which is exported as
 well, so feel free to use it, even without React. Currently it returns
-`document.documentElement?.clientHeight || window.innerHeight` or `null`.
+`window.innerHeight` in a browser and `null` in Node.
 
 ## Testing