describe android build in readme

Co-authored-by: BenjaminAmos <24301287+BenjaminAmos@users.noreply.github.com>

Author: soloturn

README.md

@@ -2,3 +2,13 @@
 A family of libraries providing a variety of core capabilities for use by games and game engines.
 
 For documentations and usage examples, see https://github.com/MovingBlocks/gestalt/wiki
+
+## Development
+To build locally, use `gradlew jar`.
+### Android Set-Up (optional)
+To build `gestalt-android`, you will need to: 
+* Download the Android SDK and use the `sdkmanager` tool to install the API 30 build tools.
+* Create a `local.properties` file in the repository root containing:
+`sdk.dir=<SDK_ROOT>`,
+where <SDK_ROOT> is the directory in which you installed the Android SDK.
+