docs: fix permissions and privilege explanation in FAQ

[liuxy600]

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Follow-up to Homebrew discussion: https://github.com/orgs/Homebrew/discussions/6617.

This PR updates the newly added FAQ section "What is the default ownership and permissions used by Homebrew" (introduced in #20946) to avoid two misleading statements:

• Clarifies that Homebrew-installed binaries run with the invoking user's privileges. Removes and adjusts wording implying binaries "inherit" admin permissions or can read/modify system locations by default.
• Fixes wording that discourages a dedicated Homebrew user account, aligning it with existing FAQ guidance that recommends a dedicated account for multi-user environments (see "Why does Homebrew say sudo is bad?": https://docs.brew.sh/FAQ#why-does-homebrew-say-sudo-is-bad).

[MikeMcQuaid]

Looks good except recommendation change.

[MikeMcQuaid]

Suggested change

By default, permissions for Homebrew-managed directories and files are `0755 (u=rwx,g=rx,o=rx)` on both macOS and Linux. This means that only the owning user (typically the installing user) can modify or replace files within the Homebrew prefix, while all users are allowed to read and execute installed binaries. On multi-user systems, Homebrew recommends managing the installation from a dedicated user account rather than running `brew` as multiple users.

By default, permissions for Homebrew-managed directories and files are `0755 (u=rwx,g=rx,o=rx)` on both macOS and Linux. This means that only the owning user (typically the installing user) can modify or replace files within the Homebrew prefix, while all users are allowed to read and execute installed binaries. On multi-user systems, Homebrew does not recommend using a dedicated user account specifically for Homebrew.

Keep this text as-is, you're changing the recommendation to be the opposite.