Update Dockerfile

Add man pages, vim and curl

Dockerfile

@@ -7,7 +7,7 @@ RUN make -C /go/src/github.com/elves/elvish get
 FROM alpine
 COPY --from=builder /go/bin/elvish /bin/elvish
 RUN adduser -D elf
-RUN apk update && apk add sudo tmux
+RUN apk update && apk add tmux man man-pages vim curl
 USER elf
 WORKDIR /home/elf
 CMD ["/bin/elvish"]