Command "Extensions: Install Extension" missing when running vscode from source

I'm trying to test the install plugin feature in the latest pre-release 0.10.7 but it doesn't show up.

![vscode_install_extension](https://cloud.githubusercontent.com/assets/1816558/12759107/986da8f2-c9c6-11e5-8d18-dc86a1bfc197.png)

I just cloned the repo and follow the steps to run vscode. I'm using Windows 8.1 x64

Am I missing something?
