Add a build and run Dockerfile (#6)

Dockerfile

@@ -0,0 +1,28 @@
+# build
+FROM golang:1.11.5-stretch AS build-env
+
+WORKDIR /src
+
+ADD . .
+
+RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -a -o app .
+
+# run
+FROM alpine
+
+RUN apk add --no-cache \
+    ca-certificates
+
+RUN addgroup -S app \
+    && adduser -S -g app app
+
+WORKDIR /home/app
+
+COPY --from=build-env /src/app .
+
+RUN chown -R app:app ./
+
+USER app
+ENV USER=app
+
+ENTRYPOINT ["./app"]

README.md

@@ -135,10 +135,26 @@ Gotify-CLI will search the following paths for a config file:
   "token": "A4ZudDRdLT40L5X",
   "url": "https://gotify.example.com"
 }
+```
+
+### Dockerfile
+The Dockerfile contains the steps necessary to build a new version of the CLI and then run it in 
+a minimal Alpine container.
+
+**Build:**
+
+```bash
+docker build -t gotify/gotify-cli .
+```
+
+**Run (this assumes your `cli.json` file is in the current working directory):**
+
+```bash
+docker run -it -v "$PWD/cli.json:/home/app/cli.json" gotify/gotify-cli:latest push -p 5 "Test from Gotify CLI"
 ```
 
  [gotify/server]: https://github.com/gotify/server
  [travis-badge]: https://travis-ci.org/gotify/cli.svg?branch=master
  [travis]: https://travis-ci.org/gotify/cli
  [badge-release]: https://img.shields.io/github/release/gotify/cli.svg
- [release]: https://github.com/gotify/cli/releases/latest
+ [release]: https://github.com/gotify/cli/releases/latest