In Tips and Tricks doc, expand -s flag

[roryokane]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew typecheck with your changes locally?
• Have you successfully run brew tests with your changes locally?

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This is a documentation-only change, so testing and brew typecheck are definitely not necessary, and I don’t think brew style is relevant either.

Affects https://docs.brew.sh/Tips-N'-Tricks#pre-download-a-file-for-a-formula

Writing the long flag here helps the user understand what the command does. The short flag is more appropriate for interactive use of brew.

[carlocab]

Thanks!

[MikeMcQuaid]

Makes sense, thanks!