Feat: dockerize app, add Docker usage description to README.md

Dockerfile

@@ -0,0 +1,14 @@
+ARG GOVERSION=1.25.5
+
+FROM --platform=$BUILDPLATFORM golang:${GOVERSION}-alpine AS builder
+ARG TARGETOS
+ARG TARGETARCH
+WORKDIR /app
+RUN --mount=type=cache,target=/go/pkg/mod/ \
+    --mount=type=bind,target=. \
+    CGO_ENABLED=0 GOOS=${TARGETOS} GOARCH=${TARGETARCH} go build -o /bin/apple-music-dl main.go
+
+FROM sambaiz/mp4box
+COPY --from=builder /bin/apple-music-dl /usr/local/bin/apple-music-dl
+COPY config.yaml ./
+ENTRYPOINT ["/usr/local/bin/apple-music-dl"]