docs: document more experiments with overlays in docs

doc/overlays/overlay3/setup.py

@@ -0,0 +1,17 @@
+from setuptools import setup, find_namespace_packages # type: ignore
+
+
+def main() -> None:
+    pkgs = find_namespace_packages('src')
+    pkg = min(pkgs)
+    setup(
+        name='hpi-overlay3',
+        zip_safe=False,
+        packages=pkgs,
+        package_dir={'': 'src'},
+        package_data={pkg: ['py.typed']},
+    )
+
+
+if __name__ == '__main__':
+    main()

doc/overlays/overlay3/src/my/twitter/_hook.py

@@ -0,0 +1,9 @@
+import importhook
+
+@importhook.on_import('my.twitter.gdpr')
+def on_import(gdpr):
+    print("EXECUTING IMPORT HOOK!")
+    tweets_orig = gdpr.tweets
+    def tweets_patched():
+        return [t.replace('gdpr', 'GDPR') for t in tweets_orig()]
+    gdpr.tweets = tweets_patched