build.sh: find d8, apktool and apksigner in ~/android-toolchain/calendar-tools, and a JDK, by default

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -150,6 +150,9 @@ Needs JDK 11+, Python 3, `d8` and `apksigner.jar` (Android SDK build-tools),
 to `com.minamp.bc` that Plexamp Lite's `tools/setup_toolchain.sh` prepares (`BC_SRC`, default
 `~/android-toolchain/bcsrc`). No Gradle.
 
+With build-tools 34's `d8.jar` and `apksigner.jar` and `apktool_2.9.3.jar` in `~/android-toolchain/calendar-tools`
+(where they are on this Mac), just `./build.sh`. Elsewhere:
+
 ```sh
 D8=d8 APKTOOL=~/apktool.jar APKSIGNER=$SDK/build-tools/34.0.0/lib/apksigner.jar ./build.sh
 # add ANDROID_JAR=$SDK/platforms/android-10/android.jar to compile against the real platform