hcl: add package comments

ast/ast.go

@@ -1,3 +1,5 @@
+// Package ast declares the types used to represent syntax trees for HCL
+// (HashiCorp Configuration Language)
 package ast
 
 import "github.com/fatih/hcl/token"

parser/parser.go

@@ -1,3 +1,5 @@
+// Package parser implements a parser for HCL (HashiCorp Configuration
+// Language)
 package parser
 
 import (

printer/printer.go

@@ -1,3 +1,4 @@
+// Package printer implements printing of AST nodes to HCL format.
 package printer
 
 import (

token/token.go

@@ -1,3 +1,5 @@
+// Package token defines constants representing the lexical tokens for HCL
+// (HashiCorp Configuration Language)
 package token
 
 import (