docs: add Homebrew install method

[Voldemorten]

Adds a Homebrew install option and restructures the Install section by platform.

brew install --cask syv-ai-dash

Changes

• macOS: documents Homebrew (brew install --cask syv-ai-dash) alongside the existing .dmg download, and notes the build is Apple Silicon (arm64) only.
• Windows / Linux: adds short download instructions for the .exe and .AppImage assets that are already published in Releases (the previous README only mentioned the macOS .dmg).

Notes

• The cask token is syv-ai-dash, not dash. The dash token is already taken in homebrew-cask by Kapeli's Dash (API documentation browser), so the vendor-prefixed form is used per Homebrew's naming convention for conflicting names.
• The cask is submitted to homebrew-cask in Add syv-ai-dash 0.11.3 (new cask) Homebrew/homebrew-cask#270120. The Homebrew line works once that cask PR is accepted, so merge order matters.
• The cask is arm64-only (matching the only macOS build) and uses auto_updates true since Dash self-updates via electron-updater.
• I added Windows/Linux instructions because those builds are in Releases. If they're experimental or unsupported and were omitted on purpose, say the word and I'll drop those sections.

I'm an external contributor, so happy to adjust wording, placement, or the token name.

[mhenrichsen]

Thanks for this! The per-platform restructuring is a nice improvement and I verified the download instructions against the latest release — Dash-0.11.3-mac-arm64.dmg (arm64-only is correct), Dash-0.11.3-win-x64.exe, and Dash-0.11.3-linux-x86_64.AppImage all line up. 👍

One blocker on the Homebrew part: brew install --cask syv-ai-dash does not resolve yet — the cask isn't in homebrew-cask core or the brew API, there's no syv-ai tap, and brew info --cask syv-ai-dash returns "No Cask with this name exists". The upstream cask PR (Homebrew/homebrew-cask#270120) is still open, so right now the documented command would error for everyone who copies it.

Plan: let's hold this until the cask actually lands. Please ping us here once Homebrew/homebrew-cask#270120 merges and we'll get this in right away. (If you'd rather land the verified .dmg/.exe/.AppImage sections sooner, we can split those out and add the Homebrew block back when the cask is live — your call.)

[Voldemorten]

Thanks for verifying the download instructions! Let's hold the whole PR until the cask lands, as you suggested. I'll ping you here the moment Homebrew/homebrew-cask#270120 merges, and we can get this in then.

For reference, that cask PR is now squashed to a single commit and just waiting on final review.