Normally, to edit settings of a theme, users must go to Customizer. But there is another way to do it. It’s creating a settings page that includes options from Customizer so that users can edit these options without going to Customizer. You can do it easily by using the MB Settings Page extension of Meta Box.
A custom settings page is essential for plugins. But for themes, the WordPress Customizer seems to be the standard. In the last few weeks, we worked on a big improvement of MB Settings Page to make it work in the Customizer. Moreover, you're now able to create network-wide settings pages.