Keybase.io download/install instructions should mention the GUI app is alpha, and still provide access to the stable CLI app

I installed the GUI app recently on a new computer, after using keybase originally nearly a year ago now, and had difficulty getting it to work. It is strange to me that https://keybase.io/download and https://keybase.io/docs/command_line/basics do not mention the alpha quality status of the GUI app, and do not mention the stable CLI app at all, and how to install it, it would be nice if they did.

Something like changing:

> Big news - we are rolling out the the Keybase filesystem. Glory to the brave. Why install? Well, that's the whole point of Keybase: you shouldn't have to keep trusting Keybase servers, which could one day be hacked/compromised/whatever. This source code is available for all.

To:

> Desktop App: For the brave, get our desktop app that bundles new features such as the [Keybase Filesystem](https://keybase.io/docs/kbfs) and a GUI around our Terminal App. Install: [macOS](https://keybase.io/docs/the_app/install_macos), [Windows](https://keybase.io/docs/the_app/install_windows), [Linux](https://keybase.io/docs/the_app/install_linux)
>
> [Terminal App](https://github.com/keybase/client/blob/master/go/README.md): For production users, get our battle tested CLI app. Available for macOS and Linux.

Start by reviewing the download page and docs/command_line/basics, then compare the existing installation pages for macOS, Windows, and Linux with the terminal app README at go/README.md. Done means the documentation distinguishes the alpha desktop app from the stable CLI app and explains how to access or install both.

Written by the indexing model from the issue text.