docs: Add configurable security policy documentation

Add documentation for custom security policy templates that allow
users to define organization-specific risk assessment guidelines.

Relates to OpenHands/software-agent-sdk#427

Author: openhands-agent

sdk/guides/security.mdx

@@ -442,6 +442,55 @@ agent = Agent(llm=llm, tools=tools, security_analyzer=security_analyzer)
 
 For more details on the base class implementation, see the [source code](https://github.com/OpenHands/software-agent-sdk/blob/main/openhands-sdk/openhands/sdk/security/analyzer.py).
 
+---
+
+## Configurable Security Policy
+
+Agents use security policies to guide their risk assessment of actions. The SDK provides a default security policy template, but you can customize it to match your specific security requirements and guidelines.
+
+<Note>
+Full configurable security policy example: [examples/01_standalone_sdk/28_configurable_security_policy.py](https://github.com/OpenHands/software-agent-sdk/blob/main/examples/01_standalone_sdk/28_configurable_security_policy.py)
+</Note>
+
+### Security Policy Example
+
+Define custom security risk guidelines for your agent:
+
+```python icon="python" expandable examples/01_standalone_sdk/28_configurable_security_policy.py
+```
+
+```bash Running the Example
+export LLM_API_KEY="your-api-key"
+cd agent-sdk
+uv run python examples/01_standalone_sdk/28_configurable_security_policy.py
+```
+
+### Using Custom Security Policies
+
+You can provide a custom security policy template when creating an agent:
+
+```python highlight={10-11}
+from openhands.sdk import Agent, LLM
+from pathlib import Path
+
+llm = LLM(
+    usage_id="agent",
+    model="anthropic/claude-sonnet-4-5-20250929",
+    api_key=SecretStr(api_key),
+)
+
+# Provide a custom security policy template file
+agent = Agent(llm=llm, tools=tools, security_policy_filename="my_security_policy.j2")
+```
+
+Custom security policies allow you to:
+- Define organization-specific risk assessment guidelines
+- Set custom thresholds for security risk levels
+- Add domain-specific security rules
+- Tailor risk evaluation to your use case
+
+The security policy is provided as a Jinja2 template that gets rendered into the agent's system prompt, guiding how it evaluates the security risk of its actions.
+
 ## Next Steps
 
 - **[Custom Tools](/sdk/guides/custom-tools)** - Build secure custom tools