Add disco build-abra-in-docker advice

Thanks @V

docs/abra/hack.md

@@ -70,6 +70,18 @@ If there's no official release for the architecture you use, you can cross-compi
 - run `git checkout <tag>`, where `<tag>` is the latest version
 - run `GOOS=<os> GOARCH=<arch> [GOARM=<arm>] make build`. You only have to use `GOARM` if you're building for ARM, this specifies the ARM version (5,6,7 etc). See [this](https://go.dev/doc/install/source#environment) for a list of all supported OS'es and architectures.
 
+### Building in Docker
+
+If you are living under a curse of constant Go environment problems, it might be easier to build `abra` using Docker:
+
+```
+sudo setenforce 0  # SELinux probably won't allow Docker to access files
+docker run -it -v $PWD:/abra golang:1.19.6 bash
+cd /abra
+. .envrc
+git config --global --add safe.directory /abra  # work around funky file permissions
+make build
+```
 
 ## Release management