docs(MADEWITHVRTK): add Percussive VR to list
docs(MADEWITHVRTK): add Percussive VR to list

A new game on Steam has been added to the list.
TMaloteaux/SteamVR_Unity_Toolkit,thestonefox/SteamVR_Unity_Toolkit,gpvigano/VRTK,gpvigano/SteamVR_Unity_Toolkit,mattboy64/SteamVR_Unity_Toolkit,red-horizon/VRTK,Fulby/VRTK,virror/VRTK,gomez-addams/SteamVR_Unity_Toolkit,adamjweaver/VRTK,Innoactive/IA-unity-VR-toolkit-VRTK,thestonefox/VRTK