Readme: add android docker build instruction

README.md

@@ -322,6 +322,15 @@ You will have to add the serialization, date_time, and regex modules to Boost wh
 
 To build: `env CC=egcc CXX=eg++ CPP=ecpp DEVELOPER_LOCAL_TOOLS=1 BOOST_ROOT=/path/to/the/boost/you/built make release-static-64`
 
+### On Linux for Android (using docker):
+
+        # Build image (select android64.Dockerfile for aarch64)
+        cd utils/build_scripts/ && docker build -f android32.Dockerfile -t monero-android .
+        # Create container
+        docker create -it --name monero-android monero-android bash
+        # Get binaries
+        docker cp monero-android:/opt/android/monero/build/release/bin .
+
 ### Building Portable Statically Linked Binaries
 
 By default, in either dynamically or statically linked builds, binaries target the specific host processor on which the build happens and are not portable to other processors. Portable binaries can be built using the following targets: