added more notes on nvm

00 Introduction.md

@@ -96,6 +96,32 @@ $ node -v
   v8.1.0
 ```
 
+Over time you will update the version of NodeJS and, as a result will end up with multiple versions installed on your computer. You can check which version are currently install using.
+```
+$ nvm ls
+           v5.1.0
+  ->       v7.3.0
+           v8.1.2
+           system
+  default -> 8.1.2 (-> v8.1.2)
+  node -> stable (-> v8.1.2) (default)
+  stable -> 8.1 (-> v8.1.2) (default)
+  iojs -> N/A (default)
+```
+As you can see there are three versions of nodejs installed and the one currently in use is v7.3.0.We can switch to a different version with `nvm use 5.1.0` for example. In the example above we are using v7.3.0 with the default is set to 8.1.2. The default version can be set using.
+```
+$ nvm alias default 8.1.2
+```
+If we no longer need one of the installed versions it can be removed.
+```
+$ nvm uninstall 5.1.0
+  Uninstalled node v5.1.0
+```
+When you update your node version you will also need to update any packages to run under the new version.
+```
+$ nvm reinstall-packages 8.1.2
+```
+
 ## Installing a Code Editor
 
 There are plenty of choices when it comes to editors. The examples in this book will use the [Visual Studio Code](https://code.visualstudio.com) editor which is available for all major platforms. If you are looking at other editors then choose one that supports JavaScript and plugins.