docs(readme): example snippet for client context manager (#657)

Author: stainless-app[bot]

README.md

@@ -428,6 +428,16 @@ client.with_options(http_client=DefaultHttpxClient(...))
 
 By default the library closes underlying HTTP connections whenever the client is [garbage collected](https://docs.python.org/3/reference/datamodel.html#object.__del__). You can manually close the client using the `.close()` method if desired, or with a context manager that closes when exiting.
 
+```py
+from lithic import Lithic
+
+with Lithic() as client:
+  # make requests here
+  ...
+
+# HTTP client is now closed
+```
+
 ## Versioning
 
 This package generally follows [SemVer](https://semver.org/spec/v2.0.0.html) conventions, though certain backwards-incompatible changes may be released as minor versions: