yo @microsoft/sharepoint fails for SPFx Dev Preview in VIsual Studio Code

The Hello World tutorial which describes the use of the Yeoman template to create a SharePoint Framework web part in Visual Studio Code suggests that the template should be installed globally.

When I follow these instructions, I am unable to create the project using yo @microsoft/sharepoint - that call gives the message:

Error @microsoft/sharepoint
You don't seem to have a generator with the name @microsoft/sharepoint installed....

I have found that installing the template locally (without the --g parameter) allows me to call the template