Add a missing section about the [foreign_library] stanza (#2771)
Add a missing section about the [foreign_library] stanza (#2771)

Signed-off-by: Andrey Mokhov <251bbb147316c69f1038239e09718efe08bbf2d1@janestreet.com>
dra27/jbuilder,janestreet/jbuilder,janestreet/jbuilder,janestreet/jbuilder,dra27/jbuilder,janestreet/jbuilder,janestreet/jbuilder,dra27/jbuilder,dra27/jbuilder,janestreet/jbuilder,dra27/jbuilder,dra27/jbuilder