change README and `llama-stack-client inference chat-completion` to use chat.completions.create#240

ashwinb merged 4 commits intollamastack:mainllamastack/llama-stack-client-python:mainfrom

mattf:move-docs-to-chat-completionsmattf/llama-stack-client-python:move-docs-to-chat-completionsCopy head branch name to clipboard