Add a simple-ish example to the doc homepage.

Otherwise it's kind of bare.

Closes: #39

docs/index.rst

@@ -2,6 +2,43 @@ An implementation-agnostic implementation of JSON reference resolution.
 
 In other words, a way for e.g. JSON Schema tooling to resolve the ``$ref`` keyword across all drafts without needing to implement support themselves.
 
+This library is meant for use both by implementers of JSON referencing-related tooling -- like JSON Schema implementations supporting the :kw:`$ref` keyword -- as well as by end-users using said implementations who wish to then configure sets of resources (like schemas) for use at runtime.
+
+The simplest example of populating a registry (typically done by end-users) and then looking up a resource from it (typically done by something like a JSON Schema implementation) is:
+
+.. testcode::
+
+    from referencing import Registry, Resource
+    import referencing.jsonschema
+
+    schema = Resource.from_contents(  # Parse some contents into a 2020-12 JSON Schema
+        {
+            "$schema": "https://json-schema.org/draft/2020-12/schema",
+            "$id": "urn:example:a-202012-schema",
+            "$defs": {
+                "nonNegativeInteger": {
+                    "$anchor": "nonNegativeInteger",
+                    "type": "integer",
+                    "minimum": 0,
+                },
+            },
+        }
+    )
+    registry = schema @ Registry()  # Add the resource to a new registry
+
+    # From here forward, this would usually be done within a library wrapping this one,
+    # like a JSON Schema implementation
+    resolver = registry.resolver()
+    resolved = resolver.lookup("urn:example:a-202012-schema#nonNegativeInteger")
+    assert resolved.contents == {
+        "$anchor": "nonNegativeInteger",
+        "type": "integer",
+        "minimum": 0,
+    }
+
+For fuller details, see the `intro`.
+
+
 .. toctree::
     :glob:
     :hidden:

docs/spelling-wordlist.txt

@@ -8,6 +8,7 @@ deserialized
 discoverability
 docstrings
 filesystem
+implementers
 instantiable
 instantiation
 iterable