chore(README.md): add award logo
chore(README.md): add award logo

The immersive perspectives award for vrtk has been added to
the README file.
Fulby/VRTK,gpvigano/SteamVR_Unity_Toolkit,gomez-addams/SteamVR_Unity_Toolkit,gpvigano/VRTK,adamjweaver/VRTK,red-horizon/VRTK,Innoactive/IA-unity-VR-toolkit-VRTK,mattboy64/SteamVR_Unity_Toolkit,thestonefox/VRTK,thestonefox/SteamVR_Unity_Toolkit,TMaloteaux/SteamVR_Unity_Toolkit