Update index.md

Author: hemang1729

docs/testing/index.md

@@ -15,11 +15,19 @@ Using [**localized assertions**](Writing_Tests/1_Traces.ipynb), `testing` always
 ## Installation
 
 ```
-pip install invariant
+pip install invariant-ai
 ```
 
 ## A quick example
 
+The example below uses `extract(...)` to detect `locations` from messages. This uses the `gpt-4o` model from OpenAI.
+
+Setup your OpenAI key as
+
+```bash
+export OPENAI_API_KEY=<your-key>
+```
+
 ```python
 # content of tests/test_weather.py
 from invariant.testing import Trace, assert_equals
@@ -97,4 +105,4 @@ Like the terminal output, the Explorer highlights the relevant ranges, but does
 
 ## Next Steps
 
-* [Quickstart Guide](./quickstart.md)
+* [Quickstart Guide](./quickstart.md)