Create README.md for camerax lib

+# CameraX support for LiveKit SDK
+
+This library provides an CameraX integration for use with the Android LiveKit SDK. This provides access to more camera functionality such as custom zoom and torch control.
+
+## Installation
+
+```groovy title="build.gradle"
+...
+dependencies {
+  implementation "io.livekit:livekit-android-camerax:<current livekit sdk release>"
+}
+```
+
+See our [release page](https://github.com/livekit/client-sdk-android/releases) for details on the current release version.