feat: add file option to cli

Since its not allways convinient to read from stdin an option to read from file is added.

Closes #451

Author: KnisterPeter

cli.js

@@ -4,20 +4,23 @@ var meow = require('meow');
 
 const cli = meow(`
   Usage
-    $ react2dts [--module-name <name> | --top-level-module] [--react-import <name>]
+    $ react2dts [--module-name <name> | --top-level-module] [--react-import <name>] [--file <path>]
 
   react2dts reads from stdin to process a file.
 
   Options
     --module-name, --name  name of the module to create
     --top-level-module     if the created module should live in top-level
     --react-import         name of the react-like library to import (default to react)
+    --file                 the file to process instead of reading from stdin
 
   Examples
     $ cat <some/react/component.jsx> |react2dts --module-name module-name
 
     $ cat <some/react/component.jsx> |react2dts --top-level-module
-`, {
+
+    $ react2dts --top-level-module --file <some/react/component.jsx>
+    `, {
   flags: {
     'module-name': {
       type: 'string',
@@ -29,6 +32,9 @@ const cli = meow(`
     'react-import': {
       type: 'string',
       default: 'react'
+    },
+    'file': {
+      type: 'string'
     }
   }
 });