Update get-dependencies command to accept entryFile as positional arg

Summary:
Small usability win when running `metro get-dependencies`. `entryFile` can now be received as an optional positional argument, as well as the existing named `--entry-file` arg.

Changelog: **[Feature]** `metro get-dependencies --entryFile <entryFile>` can now be called as `metro get-dependencies <entryFile>`

Reviewed By: motiz88

Differential Revision: D44028219

fbshipit-source-id: 2bed4e99e354f2e5c4a33cadd887c53f12665c65

Author: huntie

docs/CLI.md

@@ -32,15 +32,15 @@ Generates a JavaScript bundle containing the specified entrypoint and its descen
 
 Starts Metro on the given port, building bundles on the fly.
 
-## `get-dependencies`
+## `get-dependencies <entryFile>`
 
-Lists dependencies.
+List all dependencies that will be bundled for a given entry point.
 
 ### Options
 
 | Option | Description |
 |---|---|
-| `entry-file` | Absolute path to the root JS file |
+| `entry-file` | Absolute path to the root JS file. This can also be given as the first positional arg. |
 | `output` | File name where to store the output, ex. /tmp/dependencies.txt |
 | `platform` | The platform extension used for selecting modules |
 | `transformer` | Specify a custom transformer to be used |

packages/metro/src/commands/dependencies.js

@@ -82,8 +82,8 @@ async function dependencies(args: Args, config: ConfigT) {
 }
 
 module.exports = (): {...ModuleObject, handler: Function} => ({
-  command: 'get-dependencies',
-  desc: 'List dependencies',
+  command: 'get-dependencies [entryFile]',
+  desc: 'List all dependencies that will be bundled for a given entry point',
   builder: (yargs: Yargs) => {
     yargs.option('entry-file', {
       type: 'string',