📝 docs(flow-runner.mdx): add example code for a Flow Runner custom component

ℹ️ The example code demonstrates how to create a custom component called "Flow Runner" that runs other flows using a document as input. The code includes the implementation of the `build_config` and `build` methods.

✨ feat(flow-runner.mdx): add example code for a Flow Runner custom component to provide a practical example for users to follow

docs/docs/examples/flow-runner.mdx

@@ -29,6 +29,48 @@ We will cover how to:
 - Load a flow using the _`load_flow`_ method.
 - Configure a dropdown input field using the _`options`_ parameter.
 
+<details>
+
+<summary>Example Code</summary>
+
+```python
+from langflow import CustomComponent
+from langchain.schema import Document
+
+class FlowRunner(CustomComponent):
+display_name = "Flow Runner"
+description = "Run other flows using a document as input."
+
+    def build_config(self):
+        flows = self.list_flows()
+        flow_names = [f.name for f in flows]
+        return {"flow_name": {"options": flow_names,
+                                "display_name": "Flow Name",
+        },
+               "document": {"display_name": "Document"}
+        }
+
+
+    def build(self, flow_name: str, document: Document) -> Document:
+        # List the flows
+        flows = self.list_flows()
+        # Get the flow that matches the selected name
+        # You can also get the flow by id
+        # using self.get_flow(flow_id=flow_id)
+        flow = self.get_flow(flow_name=flow_name)
+        # Load the flow
+        tweaks = {}
+        flow = self.load_flow(flow.id, tweaks)
+        # Get the page_content from the document
+        page_content = document.page_content
+        # Use it in the flow
+        result = flow(page_content)
+        return Document(page_content=str(result))
+
+```
+
+</details>
+
 <CH.Scrollycoding rows={20} className={""}>
 
 ```python
@@ -282,8 +324,6 @@ Finally, we can add field customizations through the _`build_config`_ method. He
   Make sure that the field type is _`str`_ and _`options`_ values are strings.
 </Admonition>
 
----
-
 </CH.Scrollycoding>
 
 Done! This is what our script and custom component look like: