Make: don't destroy docker image after make, it's annoying

Makefile

@@ -1,7 +1,6 @@
 all:
 	docker build -t uhandles .
 	docker run --rm -v "${PWD}":/host uhandles
-	docker rmi uhandles
 
 docker-prep:
 	docker build -t uhandles .
@@ -17,3 +16,4 @@ build:
 
 clean:
 	rm uhandles
+	docker rmi uhandles || true

README.md

@@ -142,7 +142,7 @@ Note the newline between the two. Also, `input_2.txt` is ignored, because it doe
 ## Build
 If you're cool and already have a good working Go build environment on your system, just run `make build`.
 
-I'm not cool though, and I'm pretty lazy, 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.
+I'm not cool though, and I'm pretty lazy, 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, and `make build` will be executed within the container where all the prerequisites exist.
 
 If you're iterating, you can `make docker-prep` to create the image, `make docker-build` repeatedly to run the build, and `make docker-clean` to remove the image.