Apply suggestion from @MisterDA

* use `ADD --link`

Co-authored-by: Antonin Décimo <antonin.decimo@gmail.com>

Author: sabine

Dockerfile

@@ -43,7 +43,7 @@ COPY --from=build --link "/root/ocaml.org/_build/default/src/ocamlorg_web/bin/ma
 COPY --link playground/asset playground/asset
 
 RUN git clone https://github.com/ocaml-web/html-compiler-manuals /manual
-ADD data/v2 /v2
+ADD --link data/v2 /v2
 
 RUN git config --global --add safe.directory /var/opam-repository