Add README for human_in_the_loop samples

Author: mfateev

langgraph_samples/human_in_the_loop/README.md

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+# Human-in-the-Loop Samples
+
+Two approaches to implementing human-in-the-loop approval workflows with LangGraph and Temporal.
+
+## Samples
+
+### [approval_graph_interrupt](./approval_graph_interrupt/)
+
+Uses LangGraph's `interrupt()` function to pause graph execution.
+
+- Graph calls `interrupt(request_data)` to pause
+- Workflow detects `__interrupt__` in result, waits for signal
+- Workflow resumes graph with `Command(resume=response)`
+
+**Best for:** Standard LangGraph patterns, portable graph definitions.
+
+### [approval_wait_condition](./approval_wait_condition/)
+
+Uses `run_in_workflow=True` to access Temporal operations directly in graph nodes.
+
+- Node marked with `metadata={"run_in_workflow": True}`
+- Node uses `workflow.instance()` to access workflow
+- Node waits directly with `workflow.wait_condition()`
+
+**Best for:** Keeping all wait logic encapsulated in the graph, simpler workflow code.
+
+## Quick Comparison
+
+| Aspect | graph_interrupt | wait_condition |
+|--------|-----------------|----------------|
+| Wait logic location | Workflow | Graph node |
+| Graph portability | Higher | Lower |
+| Workflow complexity | More code | Less code |
+| Temporal API access | Indirect | Direct |