Add Docker file. Add Docker usage information.

Dockerfile

@@ -0,0 +1,14 @@
+FROM alpine:3.8 as builder
+
+WORKDIR /build
+ADD https://api.github.com/repos/anordal/shellharden/compare/master...HEAD /dev/null
+RUN apk add --no-cache cargo git
+RUN git clone https://github.com/anordal/shellharden
+RUN cd shellharden && cargo build --release
+
+
+FROM alpine:3.8
+RUN apk add --no-cache libgcc
+COPY --from=builder /build/shellharden/target/ /
+ENTRYPOINT ["/release/shellharden"]
+CMD ["--help"]

README.md

@@ -63,6 +63,16 @@ Don't apply `--transform` blindly; code review is still necessary: A script that
 
 In that unlucky case, ask yourself whether the script has any business in doing that. All too often, it's just a product of classical shellscripting, and would be better off rewritten, such as by using arrays. Even in the opposite case, say the business logic involves word splitting; that can still be done without invoking globbing. In short: There is always a better way than the forbidden syntax (if not more explicit), but some times, a human must step in to rewrite. See how, in the accompanying [how to do things safely in bash](how_to_do_things_safely_in_bash.md).
 
+Building in Docker
+To build a docker container with Shellharden:
+```
+docker build -t shellgarden:4.0 .
+```
+To run Shellharden in a Docker container:
+```
+cat shellscript.sh | docker run -i --rm sbkg0002/shellharden:4.0 ''
+```
+
 [1]: http://mywiki.wooledge.org/BashPitfalls
 [2]: https://www.shellcheck.net/
 [3]: http://stackoverflow.com/questions/41104131/tool-to-automatically-rewrite-a-bash-script-with-proper-quoting