docker cross compilation and running

docker-cross

requires recent-ish docker 

to build, first install emulation support binaries for the platforms you want to support (alternatively, if you are on an arm64 mac, you can turn on rosetta emulation in the features under development pane of docker desktop)

```
docker run --privileged --rm tonistiigi/binfmt --install all # can also pass e.g. arm64,amd64 instead of all
```

then build with a platform

```
docker build --platform linux/amd64 <dir>
```

and run with a platform

```
docker run --platform linux/amd64 <img>
```