feat(docker): add ARM64 cross-compilation support via Docker

Add Dockerfile and build script for Linux aarch64 cross-compilation targeting ARM64 devices like Raspberry Pi. Includes documentation updates explaining the build process and troubleshooting tips.

The changes enable building Palladium binaries for ARM64 architecture using cross-compilation in a Docker container, with output binaries placed in the build directory.

docker-build/Dockerfile.linux-aarch64

@@ -0,0 +1,16 @@
+FROM ubuntu:20.04
+
+ENV DEBIAN_FRONTEND=noninteractive TZ=UTC
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    build-essential libtool autotools-dev automake autoconf pkg-config \
+    bsdmainutils python3 curl ca-certificates git unzip zip file rsync \
+    make cmake patch \
+    g++-aarch64-linux-gnu binutils-aarch64-linux-gnu \
+ && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /src
+
+COPY . /src
+
+CMD ["/bin/bash"]