Update NPM installation instruction (#1556)

* Update NPM installation instruction

* further revise the doc

Author: wing328

README.md

@@ -343,20 +343,26 @@ cd /vagrant
 
 ### [1.7 - NPM](#table-of-contents)
 
-There is also an [NPM package wrapper](https://github.com/HarmoWatch/openapi-generator-cli), available.
-Please see the [docs](https://github.com/HarmoWatch/openapi-generator-cli) there for more information.
+There is also an [NPM package wrapper](https://www.npmjs.com/package/@openapitools/openapi-generator-cli) available for different platforms (e.g. Linux, Mac, Windows). (JVM is still required)
+Please see the [project's README](https://github.com/openapitools/openapi-generator-cli) there for more information.
 
 Install it globally to get the CLI available on the command line:
 
 ```sh
-npm install @harmowatch/openapi-generator-cli -g
+npm install @openapitools/openapi-generator-cli -g
 openapi-generator version
 ```
 
-Or you install it as dev-dependency like this:
+Or install a particualar OpenAPI Generator version (e.g. v3.3.3):
 
 ```sh
-npm install @harmowatch/openapi-generator-cli -D
+npm install @openapitools/[email protected] -g
+```
+
+Or install it as dev-dependency:
+
+```sh
+npm install @openapitools/openapi-generator-cli -D
 ```
 
 ## [2 - Getting Started](#table-of-contents)