temp local copy of userfunc

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

util/userfunc/README.md

@@ -0,0 +1,28 @@
+# HCL User Functions Extension
+
+This HCL extension allows a calling application to support user-defined
+functions.
+
+Functions are defined via a specific block type, like this:
+
+```hcl
+function "add" {
+  params = [a, b]
+  result = a + b
+}
+
+function "list" {
+  params         = []
+  variadic_param = items
+  result         = items
+}
+```
+
+The extension is implemented as a pre-processor for `cty.Body` objects. Given
+a body that may contain functions, the `DecodeUserFunctions` function searches
+for blocks that define functions and returns a functions map suitable for
+inclusion in a `hcl.EvalContext`. It also returns a new `cty.Body` that
+contains the remainder of the content from the given body, allowing for
+further processing of remaining content.
+
+For more information, see [the godoc reference](https://pkg.go.dev/github.com/hashicorp/hcl/v2/ext/userfunc?tab=doc).