Remove DS_Store from libgen sample

Add one-record libgen PDF parse Lance sample

Update dataset README (structure + ln -s path)

Upload Lance datasets from /tmp/dcd_xiaoyi_out

Upload Lance datasets from /tmp/dcd_libgen_out

Upload Lance datasets from /tmp/dcd_arxiv_out

Dataset card for parse demo

Upload Lance datasets from /tmp/dcd_arxiv_out

initial commit