Need readme update

[webanimal]

1. The minimum SDK is 21. It's important! So please inform about this. It can be solved if add into a manifest:
   <uses-sdk tools:overrideLibrary="com.lionzxy.trex_library" />

2. Please add to a readme an example how to add a simple view without a progress. Because a view's package depends on a lib implementation. But you realize this after an "Inflating exception" during onCreate().
   <com.lionzxy.trex_library.TRexGameView
   android:id="@+id/trexView"
   android:layout_width="match_parent"
   android:layout_height="match_parent" />