Added comments to dockerfile

Dockerfile

@@ -1,12 +1,15 @@
 FROM golang:1.16-alpine
 WORKDIR /app
 
+# Install dependencies
 COPY go.mod .
 COPY go.sum .
 RUN go mod download
 
+# Build application
 COPY *.go .
 RUN go build -o /chess-swap-backend
 
+# Run application
 EXPOSE 5000
 CMD [ "/chess-swap-backend" ]