Add instructions to set up integration testing to contributor docs (#135)

* Add instructions to set up integration testing w/ neo4j

* Clarify integration env docs

CONTRIBUTING.md

@@ -17,6 +17,15 @@ We're excited you're interested in contributing to Graphiti! This document outli
      ```
      make install
      ```
+   - To run integration tests, set the appropriate environment variables
+     ```
+     export TEST_OPENAI_API_KEY=...
+     export TEST_OPENAI_MODEL=...
+
+     export NEO4J_URI=neo4j://...
+     export NEO4J_USER=...
+     export NEO4J_PASSWORD=...
+     ```
 
 ## Making Changes