public JibContainerBuilder addLayer(List<Path> files, String pathInContainer) throws IOException {
    return addLayer(files, AbsoluteUnixPath.get(pathInContainer));
  }
Adds a new layer to the container with {@code files} as the source files and {@code
pathInContainer} as the path to copy the source files to in the container file system.

@param files the source files to copy to a new layer in the container
@param pathInContainer the path in the container file system corresponding to the {@code
    sourceFile}
@return this
@throws IOException if an exception occurred when recursively listing any directories
@throws IllegalArgumentException if {@code pathInContainer} is not an absolute Unix-style path
@see #addLayer(List, AbsoluteUnixPath)
jib-core/src/main/java/com/google/cloud/tools/jib/api/JibContainerBuilder.java