Add funcmap description in the README

README.md

@@ -38,6 +38,28 @@ $> protoc --gotemplate_out=debug=true,template_dir=/path/to/template/directory:.
 
 See [examples](./examples).
 
+## Funcmap
+
+This project uses [moul/funcmap](https://github.com/moul/funcmap) library to extend the builtin [text/template](https://golang.org/pkg/text/template) helpers.
+
+Non-exhaustive list of new helpers:
+
+* `json`
+* `prettyjson`
+* `indent`
+* `split`
+* `join`
+* `title`
+* `unexport`
+* `add`
+* `trimspace`
+* `lower`
+* `upper`
+* `rev`
+* `int`
+
+See the project for the complete list.
+
 ## Install
 
 * Install the **Go** compiler and tools from https://golang.org/doc/install