Document about binds with example (#491)

README.md

@@ -13,7 +13,8 @@
 - [Command handling](#command-handling)
   - [Switch on the command string](#switch-on-the-command-string)
   - [Attach a `Run(...) error` method to each command](#attach-a-run-error-method-to-each-command)
-- [Hooks: BeforeReset(), BeforeResolve(), BeforeApply(), AfterApply() and the Bind() option](#hooks-beforereset-beforeresolve-beforeapply-afterapply-and-the-bind-option)
+- [Hooks: BeforeReset(), BeforeResolve(), BeforeApply(), AfterApply()](#hooks-beforereset-beforeresolve-beforeapply-afterapply)
+- [The Bind() option](#the-bind-option)
 - [Flags](#flags)
 - [Commands and sub-commands](#commands-and-sub-commands)
 - [Branching positional arguments](#branching-positional-arguments)
@@ -305,7 +306,7 @@ func main() {
 
 ```
 
-## Hooks: BeforeReset(), BeforeResolve(), BeforeApply(), AfterApply() and the Bind() option
+## Hooks: BeforeReset(), BeforeResolve(), BeforeApply(), AfterApply()
 
 If a node in the CLI, or any of its embedded fields, has a `BeforeReset(...) error`, `BeforeResolve
 (...) error`, `BeforeApply(...) error` and/or `AfterApply(...) error` method, those
@@ -314,8 +315,6 @@ and after validation/assignment, respectively.
 
 The `--help` flag is implemented with a `BeforeReset` hook.
 
-Arguments to hooks are provided via the `Run(...)` method or `Bind(...)` option. `*Kong`, `*Context` and `*Path` are also bound and finally, hooks can also contribute bindings via `kong.Context.Bind()` and `kong.Context.BindTo()`.
-
 eg.
 
 ```go
@@ -341,6 +340,40 @@ func main() {
 }
 ```
 
+##  The Bind() option
+
+Arguments to hooks are provided via the `Run(...)` method or `Bind(...)` option. `*Kong`, `*Context`, `*Path` and parent commands are also bound and finally, hooks can also contribute bindings via `kong.Context.Bind()` and `kong.Context.BindTo()`.
+
+eg:
+
+```go
+type CLI struct {
+  Debug bool `help:"Enable debug mode."`
+
+  Rm RmCmd `cmd:"" help:"Remove files."`
+  Ls LsCmd `cmd:"" help:"List paths."`
+}
+
+type AuthorName string
+
+// ...
+func (l *LsCmd) Run(cli *CLI) error {
+// use cli.Debug here !!
+  return nil
+}
+
+func (r *RmCmD) Run(author AuthorName) error{
+// use binded author here
+  return nil
+}
+
+func main() {
+  var cli CLI
+
+  ctx := kong.Parse(&cli, Bind(AuthorName("penguin")))
+  err := ctx.Run()
+```
+
 ## Flags
 
 Any [mapped](#mapper---customising-how-the-command-line-is-mapped-to-go-values) field in the command structure _not_ tagged with `cmd` or `arg` will be a flag. Flags are optional by default.