docs: Linked directly to the Windows upgrade guide

Author: kumar303

README.md

@@ -25,7 +25,7 @@ You will need npm greater than version `3.0.0`:
     npm install --global npm
 
 If you're on Windows, you will also need to
-[follow these instructions](http://stackoverflow.com/questions/26908899/how-do-i-update-npm-on-windows/26908900#26908900)
+[follow these instructions](https://github.com/npm/npm/wiki/Troubleshooting#upgrading-on-windows)
 after upgrading npm.
 
 Install `web-ext`: