Provide useful output when npm install electron takes too long.

[zeke]

On slow networks, npm install electron can take quite a while. We should display something useful to users as they wait for the download to complete, both to put them at ease that something is actually happening, but also to potentially add useful info while they wait. Some ideas:

• A progress bar
• Information: platform, architecture, download size, etc
• recovery techniques if the installation fails
• ProTips™
• other info?

See also electron-userland/electron-prebuilt#236, an issue opened by @MarshallOfSound that was closed when we retired electron-prebuilt.

@bclicn articulated the problem well in electron/electron-quick-start#127 (comment)

Since this project is mainly for luring people to use electron, adding a progress bar for npm install is vital. If I followed the guide of electron.atom.io, got stuck, retired several times, googled it, and ended up here with no official solution, then how many people do you think will just give up trying Electron then?

This came up a lot today at the GitHub Universe Electron workshop.

cc @hollenberry @nathos @codebytere