WARNING:
The following guide is not needed anymore. Just install Tachyon from the Play Store.
We let this here for the records.

Setup

Download Tachyon_settings.apk and Tachyon_7_4_xxxx.apk
Add your two .APK files in your flash drive.
Plug your USB flash drive to your Shield

In your Nvidia Shield TV :

Quit Tachyon by hitting ESC
Plug USB hub in order to have enough USB port to support your flash drive, keyboard and mouse
Go to Apps menu by clicking on the center bottom icon

If it's not a clean install and you already have an older version of Tachyon installed, follow the next step:
- Uninstall Tachyon_launcher
- perform a long click on the application icon
- drag and drop it to the top of your screen (on the uninstall icon)

From the Apps menu, launch ES File Explorer
- On the left panel go to Local > Usbdrive (main panel will display the content of your thumbdrive)
- Install Tachyon_7_4_xxxx.apk

If an "Install blocked" message pop up, click on settings and allow the "Unknow sources" option. Retry to install Tachyon
Once installation is done, quit Tachyon by pressing ESC.
Go back to ES File Explorer
- Install Tachyon_settings.apk
- Once installation is done, click on Run and select the proper setup for your installation, then press Apply and Reboot

Once your reboot is complete, Tachyon will automatically start after a few seconds.