add dockerfile

Add a basic but working dockerfile.

In service of #217

To build image, 
`docker build -t mdq:1.0 .`

Sample usage:
`cat examples/hello.md | docker run --rm -i mdq:1.0 '# Greetings' `

---------

Co-authored-by: Whispard <johndoe@example.com>

.dockerignore

@@ -0,0 +1 @@
+target

Dockerfile

@@ -0,0 +1,19 @@
+FROM rust:alpine AS builder
+
+WORKDIR /usr/src/app
+RUN apk add --no-cache build-base
+
+COPY Cargo.toml Cargo.lock ./
+RUN mkdir src && echo "fn main() {}" > src/main.rs
+RUN cargo build --release && rm -rf src 
+
+COPY . .
+RUN cargo build --release
+
+FROM alpine:latest
+
+COPY --from=builder /usr/src/app/target/release/mdq .
+
+RUN chmod +x mdq
+
+ENTRYPOINT ["./mdq"]