docchange: fixed typo "Pacskage" to "Package"

<p>Additionally, before you can configure or use ADT, you must install the

Android SDK starter package, as described in <a

href="installing.html#Installing">Downloading the SDK Starter Pacskage</a>.

href="installing.html#Installing">Downloading the SDK Starter Package</a>.

Specifically, you need to install a compatible version of the Android SDK Tools

and at least one development platform. To simplify ADT setup, we recommend

installing the Android SDK prior to installing ADT. </p>