feat: install via homebrew (#9)

Add a release job that regenerates Formula/soulseek-rs.rb in michel/homebrew-tap
from the archives the binaries matrix uploads, and lead with
`brew install michel/tap/soulseek-rs` in the READMEs and on the website.

RELEASE.md

@@ -28,6 +28,9 @@ Releases are automated by [release-plz](https://release-plz.dev). You do not run
      | `soulseek-rs-vX.Y.Z-x86_64-pc-windows-msvc.zip`        |                          |
      | `soulseek-rs-vX.Y.Z-aarch64-pc-windows-msvc.zip`       |                          |
 
+   - rewrites `Formula/soulseek-rs.rb` in the `michel/homebrew-tap` repository so
+     `brew install michel/tap/soulseek-rs` picks up the new macOS and Linux archives.
+
 Both crates always share one version, one tag, and one changelog — see `release-plz.toml`.
 
 ## One-time repository setup
@@ -38,6 +41,10 @@ Both crates always share one version, one tag, and one changelog — see `releas
   [crates.io token](https://crates.io/settings/tokens) scoped to `publish-new` and
   `publish-update`. Without it the tag and GitHub release still happen, but the crates.io
   publish fails.
+- **Homebrew tap**: create a public `michel/homebrew-tap` repository, then add a
+  `HOMEBREW_TAP_TOKEN` secret — a fine-grained PAT with *Contents: read and write* on that
+  repository only. `GITHUB_TOKEN` cannot reach another repository. The formula itself is
+  generated by the workflow; nothing in the tap needs editing by hand.
 
 ## Notes