[BOOK] Chapter 15 should have adwaita-icon-theme included in macOS install command

[MonsieurRacecar]

When using the book to install libadwaita on macOS, I tried running an example (blank) application with just a titlebar and an about dialog. However, I could not add an application icon to the about dialog window because it kept appearing as the missing icon texture. After doing some more digging into this issue, it turned out that the machine must have the Homebrew package adwaita-icon-theme also installed.

As a result, the command should be changed to:
brew install libadwaita adwaita-icon-theme

Machine: iMac Retina 4K, 21.5" 2017 running macOS Ventura 13.6.7
Homebrew version is 4.3.10
GTK version is 4.14.4
Libadwaita version is 1.5.2

[Hofer-Julian]

Thanks for reporting @MonsieurRacecar!

Can you please open a pull request to fix this? :)