README example outputs Python literal, not JSON

[esnible]

Describe the bug
README.md includes a Code Examples / Variable Definition & Template Usage that concludes with the block

- model: watsonx/ibm/granite-34b-code-instruct
  input: |
    Process this input: ${USER_INPUT}
    Format the output as JSON.

Although the LLM is asked to format the output as JSON, the LLM formats the output as a Python literal (single quotes instead of double quotes).

To Reproduce
Copy the sample into a file vardef.pdl, run pdl vardef.pdl

Expected behavior
It isn't clear to me what the output should be. Should it output the user input YAML as JSON? Should it pretend it is a Python interpreter and output something? Whatever it is doing, the output isn't JSON, which means this is a bad example for top-level README.

Screenshots

pdl vardef.pdl                                        

{'output': {'source_code': '@ Suppre...eamsets/datacollector', 'repo': 'streamsets/datacollector', 'path': 'stagesupport/src/main/java/com/.../OffsetUtil.java', 'function_name': 'OffsetUtil.deserializeOffsetMap'}}

Desktop (please complete the following information):

• OS: MacOS
• Version PDL 0.1.1.dev9+g912b231.d20241218; Python 3.13.1