Twenty Sixteen: Document the twentysixteen_content_width filter.

Follow-up to [40851].

Props pmbaldha, sabernhardt.
Fixes #63646.

git-svn-id: https://develop.svn.wordpress.org/trunk@61055 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-content/themes/twentysixteen/functions.php

@@ -246,6 +246,13 @@ function twentysixteen_setup() {
  * @since Twenty Sixteen 1.0
  */
 function twentysixteen_content_width() {
+	/**
+	 * Filters Twenty Sixteen content width of the theme.
+	 *
+	 * @since Twenty Sixteen 1.0
+	 *
+	 * @param int $content_width Content width in pixels.
+	 */
 	$GLOBALS['content_width'] = apply_filters( 'twentysixteen_content_width', 840 );
 }
 add_action( 'after_setup_theme', 'twentysixteen_content_width', 0 );