serve vue app is not recognized as an internal or external code example

Example: 'vue' is not recognized as an internal or external command,

I had the same issue.
Here the quick fix.

after running the following command (as Admin)
npm install --global vue-cli

It will place the vue.cmd in the following directory
C:\Users\YourUserName\AppData\Roaming\npm

at least for me it's there.

To use vue as command in cmd. Open the cmd as admin and run the the following command.
setx /M path "%path%;%appdata%\npm"

Now restart the cmd and run the vue again. It should work just fine.