First, install the package dependencies:
npm install
Now you can compile the code:
npm run compile
After the initial compile, the source files will be watched and recompiled when changes are saved.
From a PowerShell or cmd.exe prompt, run the following command:
code --extensionDevelopmentPath="c:\path\to\vscode-powershell" .
If you allow the compiler to continue watching for file changes, you can use
the Reload Window
command found in the command palette (Ctrl+Shift+P)
so that the new source files are loaded.