Adding Bridges code as git subtree. (#2515)

* Add instructions.

* Squashed 'bridges/' content from commit 345e84a21

git-subtree-dir: bridges
git-subtree-split: 345e84a2146b56628e9888c9f5e129cb40e868a9

* Remove bridges workspace file to avoid confusing Cargo.

* Add some bridges primitives to Polkadot workspace.

* Improve docs.

polkadot/bridges/deployments/networks/OpenEthereum.Dockerfile

@@ -0,0 +1,91 @@
+FROM ubuntu:xenial AS builder
+
+# show backtraces
+ENV RUST_BACKTRACE 1
+
+ENV LAST_DEPS_UPDATE 2020-06-19
+
+# install tools and dependencies
+RUN set -eux; \
+	apt-get update && \
+	apt-get install -y file curl jq ca-certificates && \
+	apt-get install -y cmake pkg-config libssl-dev git clang libclang-dev
+
+ENV LAST_CERTS_UPDATE 2020-06-19
+
+RUN update-ca-certificates && \
+	curl https://sh.rustup.rs -sSf | sh -s -- -y
+
+ENV PATH="/root/.cargo/bin:${PATH}"
+ENV LAST_RUST_UPDATE="2020-09-09"
+RUN rustup update stable && \
+	rustup install nightly && \
+	rustup target add wasm32-unknown-unknown --toolchain nightly
+
+RUN rustc -vV && \
+    cargo -V && \
+    gcc -v && \
+    g++ -v && \
+    cmake --version
+
+WORKDIR /openethereum
+
+### Build from the repo
+ARG ETHEREUM_REPO=https://github.com/paritytech/openethereum.git
+ARG ETHEREUM_HASH=344991dbba2bc8657b00916f0e4b029c66f159e8
+RUN git clone $ETHEREUM_REPO /openethereum && git checkout $ETHEREUM_HASH
+
+### Build locally. Make sure to set the CONTEXT to main directory of the repo.
+# ADD openethereum /openethereum
+
+WORKDIR /parity-bridges-common
+
+### Build from the repo
+# Build using `master` initially.
+ARG BRIDGE_REPO=https://github.com/paritytech/parity-bridges-common
+RUN git clone $BRIDGE_REPO /parity-bridges-common && git checkout master
+
+WORKDIR /openethereum
+RUN cargo build --release --verbose || true
+
+# Then rebuild by switching to a different branch to only incrementally
+# build the changes.
+WORKDIR /parity-bridges-common
+ARG BRIDGE_HASH=master
+RUN git checkout . && git fetch && git checkout $BRIDGE_HASH
+### Build locally. Make sure to set the CONTEXT to main directory of the repo.
+# ADD . /parity-bridges-common
+
+WORKDIR /openethereum
+RUN cargo build --release --verbose
+RUN strip ./target/release/openethereum
+
+FROM ubuntu:xenial
+
+# show backtraces
+ENV RUST_BACKTRACE 1
+
+RUN set -eux; \
+	apt-get update && \
+	apt-get install -y curl
+
+RUN groupadd -g 1000 openethereum \
+  && useradd -u 1000 -g openethereum -s /bin/sh -m openethereum
+
+# switch to user openethereum here
+USER openethereum
+
+WORKDIR /home/openethereum
+
+COPY --chown=openethereum:openethereum --from=builder /openethereum/target/release/openethereum ./
+# Solve issues with custom --keys-path
+RUN mkdir -p ~/.local/share/io.parity.ethereum/keys/
+# check if executable works in this container
+RUN ./openethereum --version
+
+EXPOSE 8545 8546 30303/tcp 30303/udp
+
+HEALTHCHECK --interval=2m --timeout=5s \
+  CMD curl -f http://localhost:8545/api/health || exit 1
+
+ENTRYPOINT ["/home/openethereum/openethereum"]