add guide on how to make ones component HCL2 enabled

website/source/guides/hcl/component-object-spec/index.html.mr.erb

@@ -0,0 +1,37 @@
+---
+layout: guides
+page_title: Generating code for congig spec.
+sidebar_current: hcl
+description: |-
+  Learn how to generate the HCL2 configuration of your component easily.
+---
+
+# Packer 1.5.0 can be 
+
+From version 1.5.0 Packer can be configured using HCL2. Because Packer has so
+many builders, provisioner & post-proessors, we relied on code generation to
+iterate more easily. The good new is that you can benefit from this code
+generator to get the HCL2 spec of your component simply. Is it a Go binary
+package and is located in `cmd/mapstructure-to-hcl2`. Here are some simple
+steps you can follow to have most of the code required :
+
+Say you want to configure the Config struct of a Builder in a package located
+in `my/example-plugin/config.go`.
+
+* run `go install github.com/hashicorp/packer/cmd/mapstructure-to-hcl2`
+
+* Add `//go:generate mapstructure-to-hcl2 -type Config` at the top of
+`config.go`
+
+* run `go generate my/example-plugin`
+
+This will generate a `my/example-plugin/config.hcl2spec.go` file containing the
+configuration fields of Config. Now we only need to make Builder implement the
+interface by adding the following snippet:
+
+```go
+func (b *Builder) ConfigSpec() hcldec.ObjectSpec { return b.config.FlatMapstructure().HCL2Spec() }
+```
+
+From now one every time you add or change a field of Config you will need to
+run he `go generate` command again.