Add containerised build instructions

Containerfile

@@ -0,0 +1,9 @@
+FROM ubuntu:20.04
+
+ENV RUSTUP_HOME=/usr/local/rustup \
+    CARGO_HOME=/usr/local/cargo \
+    PATH=/usr/local/cargo/bin:$PATH
+
+RUN apt update && DEBIAN_FRONTEND=noninteractive TZ=Etc/UTC apt install -y gcc gcc-multilib cmake ffmpeg libopus-dev pkg-config libssl-dev curl mysql-client-8.0
+RUN curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --no-modify-path --profile minimal
+RUN cargo install cargo-deb