Bootstrap/Load: Ensure uses of set_time_limit are documented why.

`set_time_limit` can cause unexpected behavior so it general should be avoided. There are instances though where they should be used so those instances should be properly documented.

Props Rcrayno, ryan, kurtpayne, jorbin.
Fixes #21521. See #19487.

Built from https://develop.svn.wordpress.org/trunk@59039


git-svn-id: http://core.svn.wordpress.org/trunk@58435 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/update-core.php

@@ -962,6 +962,7 @@ function update_core( $from, $to ) {
 	global $wp_filesystem, $_old_files, $_old_requests_files, $_new_bundled_files, $wpdb;
 
 	if ( function_exists( 'set_time_limit' ) ) {
+		// Gives core update script time an additional 300 seconds(5 minutes) to finish updating large files or run on slower servers.
 		set_time_limit( 300 );
 	}