docs(FAQ.md): add more answers to common questions
docs(FAQ.md): add more answers to common questions

A few more answers have been added and the links to the YouTube
tutorial answers have been updated to the new versions.
TMaloteaux/SteamVR_Unity_Toolkit,virror/VRTK,Innoactive/IA-unity-VR-toolkit-VRTK,thestonefox/SteamVR_Unity_Toolkit,mattboy64/SteamVR_Unity_Toolkit,adamjweaver/VRTK,gomez-addams/SteamVR_Unity_Toolkit,thestonefox/VRTK,Fulby/VRTK,gpvigano/VRTK,red-horizon/VRTK,gpvigano/SteamVR_Unity_Toolkit