add Dockerfile (note)

Note that we are not adding a docker build GitHub/GitTea action
due to the extreme resource requirements of the build

Dockerfile

@@ -0,0 +1,70 @@
+# need bookworm for most up to date cmake
+FROM debian:bookworm as build
+
+RUN true && \
+    apt-get update && \
+    apt-get install -y \
+        autoconf \
+        automake \
+        autotools-dev \
+        curl \
+        python3 \
+        libmpc-dev \
+        libmpfr-dev \
+        libgmp-dev \
+        gawk \
+        build-essential \
+        bison \
+        flex \
+        texinfo \
+        gperf \
+        libtool \
+        patchutils \
+        bc \
+        zlib1g-dev \
+        libexpat-dev \
+        git \
+        && \
+    git clone --recurse-submodules https://github.com/T-head-Semi/xuantie-gnu-toolchain && \
+    cd xuantie-gnu-toolchain && \
+    ./configure --prefix=/usr/local --enable-multilib && \
+    make -j8 && \
+    cd / && \
+    rm -rf xuantie-gnu-toolchain && \
+    apt-get remove -y \
+        autoconf \
+        automake \
+        autotools-dev \
+        curl \
+        python3 \
+        libmpc-dev \
+        libmpfr-dev \
+        libgmp-dev \
+        gawk \
+        build-essential \
+        bison \
+        flex \
+        texinfo \
+        gperf \
+        libtool \
+        patchutils \
+        bc \
+        zlib1g-dev \
+        libexpat-dev \
+        git \
+        && \
+    apt-get clean && \
+    true
+
+FROM debian:bookworm
+
+COPY --from=build /usr/local/bin/* /usr/local/bin/
+COPY --from=build /usr/local/riscv64-unknown-elf /usr/local/
+
+RUN true && \
+    apt-get update && \
+    apt-get install -y --no-install-recommends \
+        cmake \
+        && \
+    apt-get clean && \
+    true