Add typescript declaration

Author: dratwas

types/index.d.ts

@@ -0,0 +1,11 @@
+declare module 'react-native-brownfield' {
+  /**
+   * A method to pop to native screen used to push React Native experience.
+   */
+  export function popToNative(animated?: boolean): void;
+
+  /**
+   * A method used to toggle iOS native back gesture and Android hardware back button.
+   */
+  export function setNativeGesturesAndButtonsEnabled(enabled: boolean): void;
+}