Add Homebrew installation instructions to documentation. (#486)

* Add Homebrew installation instructions to documentation. Closes #228.

* Update installation instructions: add headers

docs/content/installation.md

@@ -3,21 +3,38 @@ date: "2021-06-28T00:00:00+00:00"
 title: "Installation"
 ---
 
-Grizzly is currently available for Linux and MacOS systems.
+## Grizzly is currently available for Linux and MacOS systems
+
+### Installing Grizzly on Linux
 
 Download the [latest release](https://github.com/grafana/grizzly/releases).
 
 Select and download an appropriate file for your operating system. Then:
-```
+
+```bash
 sudo mv $DOWNLOADED_FILE /usr/local/bin/grr
 sudo chmod +x /usr/local/bin/grr
 ```
+
+### Installing Grizzly on macOS via Homebrew
+
+Before you begin
+Install [Homebrew](https://brew.sh) on your computer.
+
+Once Homebrew is installed, you can install Grizzly using the following command:
+
+```bash
+brew install grizzly
+```
+
+### Building from source
+
 If you wish to build the latest (as yet unreleased) version, assuming you have
 a recent Golang installed:
 
-```
+```bash
 git clone https://github.com/grafana/grizzly.git
 cd grizzly
 make dev
 sudo mv grr /usr/local/bin/grr
-```
+```