improve `uv run` instructions in README

[srabraham]

The --log-file=- is needed so that stderr gets logged to the terminal, and --config is required by the IMS server to actually start.

[github-actions[bot]]

⚠️ Optional matrix job Py:3.14.0-alpha.1 - ubuntu-latest failed ⚠️

• tox prefix: test
• exit status: 1