Add a `-h`/`--help` flag for the command line

Help flag generally shows inline documentation for the command line. This is a good way to understand the usage without opening a browser

This issue is about adding the flag.

```
$create-cosmos-app -h

Usage: create-cosmos-app [options]

Options:
-v, --version output the version number
--name name of the app
--template specify a template for the created project
....
```