Update build

Dockerfile

@@ -8,4 +8,4 @@ RUN apt-get update && apt-get install -y libjson-c-dev build-essential
 
 WORKDIR /host
 
-CMD gcc -static -o jsonsubst jsonsubst.c -ljson-c
+CMD make build

Makefile

@@ -3,5 +3,8 @@ all:
 	docker run --rm -v "${PWD}":/host jsonsubst
 	docker rmi jsonsubst
 
+build:
+	gcc -static -o jsonsubst jsonsubst.c -ljson-c
+
 clean:
 	rm jsonsubst

README.md

@@ -11,5 +11,10 @@ Or, in a pipeline of some kind...
 
 `cat input.txt | ./jsonsubst data.json | tee output.txt`
 
+## Build
+If you're cool and already have a good working C build environment on your system, just run `make build`.
+
+I'm not cool though, so I use Docker for this kind of thing, which is why it's the default make target. Just run `make` on a system with Docker running on it, and a build image will be created, `make build` executed within the container where all the prerequisites exist, and the build image will be removed after it's done.
+
 ## Notes
-No runtime dependencies, so it should run anywhere. Which means it'll run inside your quick-and-dirty Docker stuff without complaint.
+No external runtime dependencies, so it should run anywhere. Which means it'll run inside your quick-and-dirty Docker stuff without complaint.