Add instructions about thread support in Chez Scheme to INSTALL.md
Add instructions about thread support in Chez Scheme to INSTALL.md

I encountered a difficult-to-diagnose error while bootstrapping Idris 2, and these instructions fixed it for me.
mmhelloworld/idris-jvm,mmhelloworld/idris-jvm,mmhelloworld/idris-jvm,mmhelloworld/idris-jvm,mmhelloworld/idris-jvm,mmhelloworld/idris-jvm