DOC: Add station_info and StationLookup to docs.

Includes a basic doctestable example.

src/metpy/io/__init__.py

@@ -1,11 +1,15 @@
 # Copyright (c) 2015,2016,2018,2021 MetPy Developers.
 # Distributed under the terms of the BSD 3-Clause License.
 # SPDX-License-Identifier: BSD-3-Clause
-"""Classes for reading various file formats.
+"""Tools for reading various file formats.
 
-These classes are written to take both file names (for local files) or file-like objects;
-this allows reading files that are already in memory (using :class:`python:io.StringIO`)
-or remote files (using :func:`~python:urllib.request.urlopen`).
+Classes supporting formats are written to take both file names (for local files) or file-like
+objects; this allows reading files that are already in memory
+(using :class:`python:io.StringIO`) or remote files
+(using :func:`~python:urllib.request.urlopen`).
+
+`station_info` is an instance of `StationLookup` to find information about station locations
+(e.g. latitude, longitude, altitude) from various sources.
 """
 
 from .gempak import *  # noqa: F403

src/metpy/io/station_data.py

@@ -121,8 +121,18 @@ def _read_airports_file(input_file=None):
                          }).to_dict()
 
 
+@exporter.export
 class StationLookup(Mapping):
-    """Look up station information from multiple sources."""
+    """Look up station information from multiple sources.
+
+    This class follows the `Mapping` protocol with station ID as the key. This makes it
+    possible to e.g. iterate over all locations and get all of a certain criteria:
+
+    >>> import metpy.io
+    >>> conus_stations = [s for s in metpy.io.station_info if s.startswith('K')]
+    >>> conus_stations[:3]
+    ['KEET', 'K8A0', 'KALX']
+    """
 
     @cached_property
     def tables(self):