Add a setting to WordPress customizer

customizer.php

		// This example is for a section called theme options, with a setting for copyright text
    $wp_customize->add_section( 'theme_options_section' , array(
		    'title'      => __('Theme Options','themename'),
		    'priority'   => 30,
		) );


		$wp_customize->add_setting( 'copyright_text' , array(
		    'default' => 'Default text here'
    		) );



		$wp_customize->add_control(
		'copyright_setting', 
			array(
				'label'    => __( 'Copyright Text', 'themename' ),
				'section'  => 'theme_options_section',
				'settings' => 'copyright_text',
				'type'     => 'textarea'
			)
		);