Add rsync, m4 to the generated images

it's hard to use opam without installing them :)

Dockerfile

@@ -25,7 +25,7 @@ RUN rm -rf /src
 FROM alpine:3.11 as target
 LABEL Description="Minimal OCaml + opam Alpine container" Vendor="OCamlPro"
 
-RUN apk add gcc libc-dev make curl git sudo patch
+RUN apk add gcc libc-dev make curl git sudo patch rsync m4
 COPY --from=compilation /usr/local /usr/local
 
 RUN addgroup -S ocaml && adduser -S ocaml -G ocaml -s /bin/sh