Harrison/add react chain (#24)

from https://arxiv.org/abs/2210.03629

still need to think if docstore abstraction makes sense

tests/integration_tests/chains/test_react.py

@@ -0,0 +1,13 @@
+"""Integration test for self ask with search."""
+
+from langchain.chains.react.base import ReActChain
+from langchain.llms.openai import OpenAI
+
+
+def test_react() -> None:
+    """Test functionality on a prompt."""
+    llm = OpenAI(temperature=0)
+    react = ReActChain(llm=llm)
+    question = "Were Scott Derrickson and Ed Wood of the same nationality?"
+    output = react.run(question)
+    assert output == "yes"