ARROW-5416: [Website] Add Homebrew to project installation page

Author: Neal Richardson <neal.p.richardson@gmail.com>

Closes #4401 from nealrichardson/homebrew-website and squashes the following commits:

c35aa92f <Neal Richardson> @kou's requested changes
40e42a2d <Neal Richardson> Add homebrew to install page
diff --git a/install.md b/install.md
index fd00ce5..06959c4 100644
--- a/install.md
+++ b/install.md
@@ -69,6 +69,21 @@
 These include the Apache Arrow and Apache Parquet C++ binary libraries bundled
 with the wheel.
 
+### C++ and GLib (C) Packages on Homebrew (Unofficial)
+
+On macOS, you can install the C++ library using
+[Homebrew][17]:
+
+```shell
+brew install apache-arrow
+```
+
+and GLib (C) package with:
+
+```shell
+brew install apache-arrow-glib
+```
+
 ### C++ and GLib (C) Packages for Debian GNU/Linux, Ubuntu and CentOS (Unofficial)
 
 We have provided APT and Yum repositories for Apache Arrow C++ and
@@ -224,3 +239,4 @@
 [14]: {{site.data.versions['current'].sha256}}
 [15]: {{site.data.versions['current'].sha512}}
 [16]: https://github.com/msys2/MINGW-packages/tree/master/mingw-w64-arrow
+[17]: https://brew.sh/