[docs] Improve CLI copy

[stevhliu]

Improves CLI copy to be more clear, consistent, brief, and actionable (adapted from https://github.com/vercel/vercel/blob/main/packages/cli/.agents/skills/cli-ux/references/copy.md). See some selected examples below:

Before	After
When not using an editable install, the path to the Transformers repo.	Path to the Transformers repo when not using an editable install
Enable permissive CORS.	Allow cross-origin requests from any origin
Seconds before idle model is unloaded. Ignored when force_model is set.	Unload idle models after this many seconds; ignored with a fixed model
Whether or not to allow for custom models defined on the Hub in their own modeling files. Use only if you've reviewed the code as it will execute on your local machine	Allow custom model code from the Hub to run locally after you've reviewed it
Path to a local generation config file or to a HuggingFace repo containing a generation_config.json file. Other generation settings passed as CLI arguments will be applied on top of this generation config.	Local path or Hub repo containing generation_config.json; CLI generation settings override it
When not using an editable install, the path to the Transformers repo.	Path to the Transformers repo when not using an editable install

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[github-actions]

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CI recap

Dashboard: View test results in Grafana
Latest run: 29370756571:1
Result: success | Jobs: 2 | Tests: 10 | Failures: 0 | Duration: 39s