The daml damlc docs command is looking for Haddock-style annotations. However, see this caveat.
For the following:
-- | an asset is a thing that can be owned by a user
template Asset
  with
    issuer : Party
      -- ^ the issuer of the asset
    owner  : Party
    name   : Text
The command:
daml damlc docs -o docs --doc-ext md daml/Main.daml
Generates:
You can see examples in the Daml Standard Library and the Splice code base.
