Make the README more copy-pastable

The README has many sections where I can't copy and paste the commands:

```
$ cd examples/hello
$ docker build -t app .
...

$ docker run -it -p 8080:8080 --name demo --rm app
Listening on :8080
```

It would be nice if the README allowed me to copy and paste the commands, like this:

```sh
cd examples/hello
docker build -t app .
# ...

docker run -it -p 8080:8080 --name demo --rm app
# Listening on :8080
```