chore(docs): add correct --appPath option description

This PR brings description of --appPath option missing from the
d3dd42e3 original commit and is a very trivial PR. The reasoning behind this PR is that `--help` option for generator prints outs misleading description of two different options:
```bash
yo angular --help
```
```bash
--appPath             # Generate CoffeeScript instead of JavaScript ...
--coffee              # Generate CoffeeScript instead of JavaScript ...
```
After this change the `--help` option will correctly print option purpose:
```bash
--appPath             # Allow to choose where to write the files ...
--coffee              # Generate CoffeeScript instead of JavaScript ...
```
I've signed CLA on code.google.com already under my github.com username.