adding two Dockerfiles, one for base image and the other for multistage build, and circleci config to test

Signed-off-by: Vanessa Sochat <vsochat@stanford.edu>

docker/Dockerfile

@@ -0,0 +1,4 @@
+FROM nushell/nu-base as base
+FROM rust:1.37-slim
+COPY --from=base /usr/local/bin/nu /usr/local/bin/nu
+ENTRYPOINT ["nu"]

docker/Dockerfile.nu-base

@@ -0,0 +1,17 @@
+FROM rust:1.37-slim
+
+# docker build -t nushell/nu-base .
+# docker run -it nushell/nu-base
+
+ENV DEBIAN_FRONTEND noninteractive
+RUN apt-get update && apt-get install -y libssl-dev \
+    libxcb-composite0-dev \
+    libx11-dev \
+    pkg-config && \
+    mkdir -p /code
+
+ADD . /code
+WORKDIR /code
+RUN cargo build --release && cargo run --release && \
+    cp target/release/nu /usr/local/bin
+ENTRYPOINT ["nu"]