Tweak docker(compose) files (can't test them yet) and add a little backend documentation

backend/Dockerfile

@@ -1,24 +0,0 @@
-FROM paritytech/ci-linux:production as builder
-
-ARG PROFILE=release
-WORKDIR /app
-
-COPY . .
-
-RUN cargo build --${PROFILE} --bins
-
-# MAIN IMAGE FOR PEOPLE TO PULL --- small one#
-FROM debian:buster-slim
-LABEL maintainer="Parity Technologies"
-LABEL description="Polkadot Telemetry backend, static build"
-
-ARG PROFILE=release
-WORKDIR /usr/local/bin
-
-COPY --from=builder /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
-COPY --from=builder /app/target/$PROFILE/telemetry /usr/local/bin
-RUN apt-get -y update && apt-get -y install openssl && apt-get autoremove -y && apt-get clean && rm -rf /var/lib/apt/lists/
-
-EXPOSE 8000
-
-ENTRYPOINT ["telemetry"]