docs: update integration api refs (#25195)

- [x] toolkits
- [x] retrievers (in this repo)

libs/community/langchain_community/retrievers/wikipedia.py

@@ -10,9 +10,66 @@ from langchain_community.utilities.wikipedia import WikipediaAPIWrapper
 class WikipediaRetriever(BaseRetriever, WikipediaAPIWrapper):
     """`Wikipedia API` retriever.
 
-    It wraps load() to get_relevant_documents().
-    It uses all WikipediaAPIWrapper arguments without any change.
-    """
+    Setup:
+        Install the ``wikipedia`` dependency:
+
+        .. code-block:: bash
+
+            pip install -U wikipedia
+
+    Instantiate:
+        .. code-block:: python
+
+            from langchain_community.retrievers import WikipediaRetriever
+
+            retriever = WikipediaRetriever()
+
+    Usage:
+        .. code-block:: python
+
+            docs = retriever.invoke("TOKYO GHOUL")
+            print(docs[0].page_content[:100])
+
+        .. code-block:: none
+
+            Tokyo Ghoul (Japanese: 東京喰種（トーキョーグール）, Hepburn: Tōkyō Gūru) is a Japanese dark fantasy
+
+    Use within a chain:
+        .. code-block:: python
+
+            from langchain_core.output_parsers import StrOutputParser
+            from langchain_core.prompts import ChatPromptTemplate
+            from langchain_core.runnables import RunnablePassthrough
+            from langchain_openai import ChatOpenAI
+
+            prompt = ChatPromptTemplate.from_template(
+                \"\"\"Answer the question based only on the context provided.
+
+            Context: {context}
+
+            Question: {question}\"\"\"
+            )
+
+            llm = ChatOpenAI(model="gpt-3.5-turbo-0125")
+
+            def format_docs(docs):
+                return "\\n\\n".join(doc.page_content for doc in docs)
+
+            chain = (
+                {"context": retriever | format_docs, "question": RunnablePassthrough()}
+                | prompt
+                | llm
+                | StrOutputParser()
+            )
+
+            chain.invoke(
+                "Who is the main character in `Tokyo Ghoul` and does he transform into a ghoul?"
+            )
+
+        .. code-block:: none
+
+             'The main character in Tokyo Ghoul is Ken Kaneki, who transforms into a ghoul after receiving an organ transplant from a ghoul named Rize.'
+    """  # noqa: E501
 
     def _get_relevant_documents(
         self, query: str, *, run_manager: CallbackManagerForRetrieverRun