Add docker builds

Dockerfile

@@ -0,0 +1,14 @@
+FROM rust:latest AS builder
+WORKDIR /makedot
+
+RUN mkdir src && echo "fn main() {}" > src/main.rs 
+COPY ./Cargo.lock ./
+COPY ./Cargo.toml ./
+RUN cargo fetch 
+RUN cargo build --release 
+RUN rm -r src/
+COPY ./src ./src
+RUN cargo build --release
+
+FROM scratch
+COPY --from=builder /makedot/target/release/makedot /makedot

Readme.md

@@ -15,4 +15,10 @@ makedot ./hack/ci/Makefile | dot -T svg -o ./graph.svg
 git clone --depth 1 https://github.com/VOID404/makedot.git
 cargo build --release
 ./target/release/makedot
+```
+
+Alternatively you can build inside docker:
+```sh
+docker build --output=./target/release .
+./target/release/makedot
 ```

src/main.rs

@@ -18,6 +18,8 @@ fn main() {
         std::process::exit(1);
     });
 
+    eprintln!("Starting at {}", path);
+
     let (makefiles, externals) = Makefile::walk_from(path);
 
     let mut id = IDGen::new("cluster_");