Initial project import

tools/v/vlib/cli/README.md

@@ -0,0 +1,65 @@
+## Description
+
+`cli` is a command line option parser, that supports
+declarative subcommands, each having a separate set of options.
+
+See also the `flag` module, for a simpler command line option parser,
+that supports only options.
+
+## Example
+
+```v
+module main
+
+import os
+import cli
+
+fn main() {
+	mut app := cli.Command{
+		name:        'example-app'
+		description: 'example-app'
+		execute:     fn (cmd cli.Command) ! {
+			println('hello app')
+			return
+		}
+		commands:    [
+			cli.Command{
+				name:    'sub'
+				alias:   's'
+				execute: fn (cmd cli.Command) ! {
+					println('hello subcommand')
+					return
+				}
+			},
+		]
+	}
+	app.setup()
+	app.parse(os.args)
+}
+```
+
+Subcommands can set `alias` to accept a shorter invocation token, for example
+`example-app s`.
+
+## Help layout
+
+`--help` is generated automatically. Beyond `Usage:`, `Flags:` and `Commands:`
+the output picks up extra sections when the relevant `Command` fields are
+populated:
+
+- **`Inherited flags:`** — flags inherited from any ancestor through
+  `Flag.global`. Renders separately from local flags so a sub-command's
+  own surface stays readable.
+- **Grouped commands** — set `group` on a sub-command to lift it out of
+  the default `Commands:` block into a section named after the group.
+  The group string is rendered verbatim followed by `:`, so capitalisation
+  is the caller's choice. Sub-commands sharing a group keep their
+  declaration order.
+- **`Examples:`** — set `examples []string` on a `Command`; each entry
+  becomes one indented line.
+- **`Learn more:`** — set `learn_more string`; newlines split the block
+  into separate lines.
+
+Sections that have nothing to render are simply omitted, so existing apps
+see no change unless they opt in by setting these fields. See
+`examples/cli_groups.v` for a runnable program that exercises all of them.