Add build/ subfolder to help build overlays out of AOSP
diff --git a/build/build.sh b/build/build.sh
new file mode 100644
index 0000000..5be85cf
--- /dev/null
+++ b/build/build.sh
@@ -0,0 +1,21 @@
+#!/bin/bash
+
+set -e
+
+if ! which aapt > /dev/null;then
+    echo "Please install aapt (apt install aapt should do)"
+    exit 1
+fi
+
+cd "$(dirname "$(readlink -f -- $0)")"
+
+find .. -name Android.mk |while read f;do
+    name="$(sed -nE 's/LOCAL_PACKAGE_NAME.*:\=\s*(.*)/\1/p' "$f")"
+    grep -q treble-overlay <<<$name || continue
+    echo "Generating $name"
+
+    path="$(dirname "$f")"
+    aapt package -f -F ${name}-unsigned.apk -M $path/AndroidManifest.xml -S $path/res -I /build/apps/platforms/android-27/android.jar
+    LD_LIBRARY_PATH=./signapk/ java -jar signapk/signapk.jar keys/platform.x509.pem keys/platform.pk8 ${name}-unsigned.apk ${name}.apk
+    rm -f ${name}-unsigned.apk
+done