This is a first draft of HCLv2 docs - I added the details under hcl2 doc with some minimal info highlighting the hcl2 introductions.
As a longer term strategy, we'll want to mimic the Packer HCL docs structure that details all the blocks and allowed expressions/functions in greater details. However, given that the exact functions and templating syntax is still somewhat influx, I opt to push that to another time.
