docs: add reference for npx initialization (#310)

* (Chore) Update README.md

* docs: add reference for npx initialization

---------

Co-authored-by: Ulises Gascón <ulisesgascongonzalez@gmail.com>

README.md

@@ -13,6 +13,12 @@
 $ npm install -g express-generator
 ```
 
+You can also run the application generator with the `npx` command (available since Node.js 8.2.0).
+
+```sh
+$ npx express-generator
+```
+
 ## Quick Start
 
 The quickest way to get started with express is to utilize the executable `express(1)` to generate an application as shown below: