docs: Adds module-level doc to altair.datasets

- Multiple **brief** examples, for a taste of the public API
  - See (#3763)
- Refs to everywhere a first-time user may need help from
- Also aligned the (`Loader`|`load`) docs w/ eachother and the new phrasing here

altair/datasets/__init__.py

@@ -1,3 +1,64 @@
+"""
+Load example datasets **remotely** from `vega-datasets`_.
+
+Provides over **70+** datasets, used throughout our `Example Gallery`_.
+
+You can learn more about each dataset at `datapackage.md`_.
+
+Examples
+--------
+Load a dataset as a ``DataFrame``/``Table``::
+
+    from altair.datasets import load
+
+    load("cars")
+
+.. note::
+   Requires installation of either `polars`_, `pandas`_, or `pyarrow`_.
+
+Get the remote address of a dataset and use directly in a :class:`altair.Chart`::
+
+    import altair as alt
+    from altair.datasets import url
+
+    source = url("co2-concentration")
+    alt.Chart(source).mark_line(tooltip=True).encode(x="Date:T", y="CO2:Q")
+
+.. note::
+   Works without any additional dependencies.
+
+For greater control over the backend library use::
+
+    from altair.datasets import Loader
+
+    load = Loader.from_backend("polars")
+    load("penguins")
+    load.url("penguins")
+
+This method also provides *precise* <kbd>Tab</kbd> completions on the returned object::
+
+    load("cars").<Tab>
+    #            bottom_k
+    #            drop
+    #            drop_in_place
+    #            drop_nans
+    #            dtypes
+    #            ...
+
+.. _vega-datasets:
+    https://github.com/vega/vega-datasets
+.. _Example Gallery:
+    https://altair-viz.github.io/gallery/index.html#example-gallery
+.. _datapackage.md:
+    https://github.com/vega/vega-datasets/blob/main/datapackage.md
+.. _polars:
+    https://docs.pola.rs/user-guide/installation/
+.. _pandas:
+    https://pandas.pydata.org/docs/getting_started/install.html
+.. _pyarrow:
+    https://arrow.apache.org/docs/python/install.html
+"""
+
 from __future__ import annotations
 
 from typing import TYPE_CHECKING
@@ -22,7 +83,9 @@
 
 load: _Load[Any, Any]
 """
-For full IDE completions, instead use:
+Get a remote dataset and load as tabular data.
+
+For full <kbd>Tab</kbd> completions, instead use:
 
     from altair.datasets import Loader
     load = Loader.from_backend("polars")

altair/datasets/_loader.py

@@ -29,7 +29,7 @@
 
 class Loader(Generic[IntoDataFrameT, IntoFrameT]):
     """
-    Load examples **remotely** from `vega-datasets`_, with caching.
+    Load example datasets **remotely** from `vega-datasets`_, with caching.
 
     A new ``Loader`` must be initialized by specifying a backend: