Improve prompt engineering quickstart for new users

src/snippets/langsmith/set-workspace-secrets.mdx

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+In the [LangSmith UI](https://smith.langchain.com) for your workspace, ensure that your OpenAI API key is set as a [workspace](/langsmith/administration-overview#workspace-secrets).
+
+1. Navigate to <Icon icon="gear" /> **Settings** and then move to the **Secrets** tab.
+1. On the **Workspace Secrets** page, select **Add secret** and enter the `OPENAI_API_KEY` and your API key as the **Value**.
+1. Select **Save secret**.
+
+<Note> When adding workspace secrets in the LangSmith UI, make sure the secret keys match the environment variable names expected by your model provider.</Note>