Mention Mac-specific needs for building for Android
TBR @abarth
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index df3fd79..dd7b899 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -40,10 +40,17 @@
Currently we support building on Linux only, for an Android target and for a headless Linux
target. Building on MacOS for Android, iOS, and a head-less MacOS target is coming soon.
-### Android (cross-compiling from Linux)
+### Android (cross-compiling from Mac or Linux)
-* (Only the first time) `./tools/android/download_android_tools.py`
-* (Only the first time) `sudo ./build/install-build-deps-android.sh`
+## The first time
+
+* `./tools/android/download_android_tools.py`
+* On Linux: `sudo ./build/install-build-deps-android.sh`
+* On Mac: Install Oracle's Java JDK, version 1.7 or later.
+* On Mac: Install "ant": `brew install ant`.
+
+## Building
+
* `./sky/tools/gn --android`
* `ninja -C out/android_Debug`
* `./sky/tools/shelldb start out/android_Debug/ examples/hello_world/lib/main.dart`
