Add documentation for load_workflow() (#306)

Add documentation for `load_workflow()` to demonstrate the process of creating and using workflows directly from code.

Closes [AIQ-1207](https://jirasw.nvidia.com/browse/AIQ-1207)

## By Submitting this PR I confirm:
- I am familiar with the [Contributing Guidelines](https://github.com/NVIDIA/AIQToolkit/blob/develop/docs/source/resources/contributing.md).
- We require that all contributors "sign-off" on their commits. This certifies that the contribution is your original work, or you have rights to submit it under the same license, or a compatible license.
  - Any contribution which contains commits that are not Signed-Off will not be accepted.
- When the PR is ready for review, new or existing tests cover these changes.
- When the PR is ready for review, the documentation is up to date with these changes.

Authors:
  - Yuchen Zhang (https://github.com/yczhang-nv)

Approvers:
  - David Gardner (https://github.com/dagardner-nv)

URL: #306

Author: yczhang-nv

docs/source/workflows/run-workflows.md

@@ -73,4 +73,17 @@ Refer to `aiq serve --help` for more information on how to customize the server.
 
 ## Using the Python API
 
-Using the Python API for running workflows is outside the scope of this document. Refer to the Python API documentation for the {py:class}`~aiq.runtime.runner.AIQRunner` class for more information.
+The toolkit offers a programmatic way to execute workflows through its Python API, allowing you to integrate workflow execution directly into your Python code. Here's how to use it:
+
+```python
+    async with load_workflow(config_file) as workflow:
+        async with workflow.run(input_str) as runner:
+            result = await runner.result(to_type=str)
+```
+
+In this example:
+- `config_file`: A string path pointing to your workflow YAML file
+- `input_str`: A string containing the input for your workflow
+- The `workflow.run(input_str)` method returns an instance of {py:class}`~aiq.runtime.runner.AIQRunner`
+
+For detailed information about the `AIQRunner` class and its capabilities, please refer to the Python API documentation for the {py:class}`~aiq.runtime.runner.AIQRunner` class.