Generate README.md for catalogs and collections

[hombit]

Feature request

It would be really great if we could add an ability to generate human-readable README.md files for catalogs and collections. I also propose making the generation of this file the default behavior for catalog and collection outputs from hats-import and adding an option for that for LSDB. Markdown files are human-readable, even in raw form, and would be rendered by IDEs, Jupyter, Hugging Face, GitHub, etc. In the future, we can also consider generating an index.html page for HTTP-based hosting of the catalogs.

This is how the README.md may look like (my comments are in "[]"):

[This YAML metadata on the top of the readme is used by Hugging Face and datasets library, for both local and remote locations. It should be opt-in]

---

configs:

• config_name: default
  data_dir: "ztf_dr23_lc-hats/dataset/"
• config_name: margin_10arcs
  data_dir: "ztf_dr23_lc-hats_margin_10arcsec/dataset/"
• config_name: index_objectid
  data_dir: "ztf_dr23_lc-hats_index_objectid/dataset/"

---

Zwicky Transient Facility Data Release 23 (lightcurves) catalog

This is the Zwicky Transient Facility Data Release 23 (lightcurves) catalog in HATS format. [OR USER-PROVIDED DESCRIPTION]

You can open the catalog using LSDB, see details at https://docs.lsdb.io:

import lsdb
lsdb.open_catalog(<path-to-the-catalog>)

Auxiliary catalogs

• 10-arcsecond margin catalog: ztf_dr23_lc-hats_margin_10arcsec/
• Secondary index catalog for column objectid: ztf_dr23_lc-hats_index_objectid/

Catalog metadata

Number of rows	Number of columns	Number of partitions	Size on disk
4,973,896,193	13	9,933	8.0 TiB

Columns

Right accession column: objra.
Declination column: objdec.
Primary HEALPix column, order 29: _healpix_29.

[Some additional columns could go here, when we support descriptions, etc]

Name	_healpix_19	_healpix_9	objectid	filterid	fieldid	rcid	objra	objdec	nepochs	lightcurve.hmjd	lightcurve.mag	lightcurve.magerr	lightcurve.clrcoeff	lightcurve.catflags
Data type	int64	int32	int64	int8	int16	int8	float32	float32	int64	list[float64]	list[float32]	list[float32]	list[float32]	list[int32]
Default?	no	no	yes	yes	no	no	yes	yes	no	yes	yes	yes	yes	yes
Nested?	no	no	no	no	no	no	no	no	no	lightcurve	lightcurve	lightcurve	lightcurve	lightcurve
First row	175802814	167	1447212400010477	2	1447	47	44.042023	1.264162	1	[58761.42485]	[20.727491]	[0.2088]	[0.124223]	[0]

Sky Maps

[I put plots to the end, because we are probably going to embed them, here I just uploaded to github]

Angular density map

Partition map

[hombit]

@nevencaplar proposed adding a cone-search example

[hombit]

@delucchi-cmu proposed to add min-max values to the column table