Document Homebrew package

Resolves #2329

Documents the recently added `lighthouse` Homebrew formula.

book/src/SUMMARY.md

@@ -10,6 +10,7 @@
     * [Build from Source](./installation-source.md)
     * [Raspberry Pi 4](./pi.md)
     * [Cross-Compiling](./cross-compiling.md)
+    * [Homebrew](./homebrew.md)
 * [Key Management](./key-management.md)
     * [Create a wallet](./wallet-create.md)
     * [Create a validator](./validator-create.md)

book/src/homebrew.md

@@ -0,0 +1,36 @@
+# Homebrew package
+
+Lighthouse is available on Linux and macOS via the [Homebrew package manager](https://brew.sh).
+
+Please note that this installation method is maintained by the Homebrew community.
+It is not officially supported by the Lighthouse team.
+
+### Installation
+
+Install the latest version of the [`lighthouse`][formula] formula with:
+
+```bash
+brew install lighthouse
+```
+
+### Usage
+
+If Homebrew is installed to your `PATH` (default), simply run:
+
+```bash
+lighthouse --help
+```
+
+Alternatively, you can find the `lighthouse` binary at:
+
+```bash
+"$(brew --prefix)/bin/lighthouse" --help
+```
+
+### Maintenance
+
+The [formula] is kept up-to-date by the Homebrew community and a bot that lists for new releases.
+
+The package source can be found in the [homebrew-core](https://github.com/Homebrew/homebrew-core/blob/master/Formula/lighthouse.rb) repo.
+
+  [formula]: https://formulae.brew.sh/formula/lighthouse

book/src/installation.md

@@ -8,6 +8,10 @@ There are three core methods to obtain the Lighthouse application:
 - [Docker images](./docker.md).
 - [Building from source](./installation-source.md).
 
+The community maintains additional installation methods (currently only one).
+
+- [Homebrew package](./homebrew.md).
+
 Additionally, there are two extra guides for specific uses:
 
 - [Rapsberry Pi 4 guide](./pi.md).