docs: Add description of Homebrew's official formula (#1421)

* docs: Add description of Homebrew's official formula

* Update index.mdx

Author: rinsuki

docs/src/docs/usage/install/index.mdx

@@ -49,10 +49,12 @@ and is constantly being improved. For any problems with `golangci-lint`, check o
 You can install a binary release on macOS using [brew](https://brew.sh/):
 
 ```sh
-brew install golangci/tap/golangci-lint
-brew upgrade golangci/tap/golangci-lint
+brew install golangci-lint
+brew upgrade golangci-lint
 ```
 
+Note: previously we use [tap](https://github.com/golangci/homebrew-tap), but it is obsoleted. We recommend using official formula instead of an obsolete tap.
+
 It can also be installed through [macports](https://www.macports.org/)
 The macports installation mode is community driven, and not officially maintained by golangci team.