Add support for using podman if docker is unavailable

Makefile

@@ -1,4 +1,5 @@
 TIMESTAMP := $(shell date -u +"%Y%m%d%H%M%S")
+CONTAINER_CMD := $(shell { command -v docker || command -v podman; })
 
 .PHONY: clean setup
 
@@ -10,11 +11,11 @@ clean:
  rm ./firmware/*.uf2
 
 firmware/%-left.uf2 firmware/%-right.uf2: config/adv360.keymap
- docker run --rm -it --name zmk \
+ $(CONTAINER_CMD) run --rm -it --name zmk \
  -v $(PWD)/firmware:/app/firmware \
  -v $(PWD)/config:/app/config:ro \
  -e TIMESTAMP=$(TIMESTAMP) \
  zmk
 
 setup: Dockerfile bin/build.sh config/west.yml
- docker build --tag zmk --file Dockerfile .
+ $(CONTAINER_CMD) build --tag zmk --file Dockerfile .