Fix broken custom prompt template example in README

[jtdub]

Summary

README.md:236-241 shows passing prompt_template=template to GPTWorkflowRemediation(...), but the constructor does not accept this parameter. The example will raise a TypeError.

Current README Example (Broken)

template = PromptTemplate(template=custom_template)
wfr = GPTWorkflowRemediation(
    running_config=running,
    generated_config=generated,
    prompt_template=template  # <-- TypeError: unexpected keyword argument
)

Fix

This depends on resolving issue #9 (integrating PromptTemplate into the workflow). Once GPTWorkflowRemediation accepts a prompt_template parameter, update the README to match the actual API.