code: public static Closeable mountReal(File realRoot, VirtualFile mountPoint) throws IOException {
          return doMount(new RealFileSystem(realRoot), mountPoint);
      }
docs: Create and mount a real file system, returning a single handle which will unmount and close the filesystem when
  closed.
  
  @param realRoot   the real filesystem root
  @param mountPoint the point at which the filesystem should be mounted
  @return a handle
  @throws IOException if an error occurs