Move copyright/license headers to CONTRIBUTING.md

These are more like a general contribution guidelines for the new files
added to the php-src repository.

Author: petk

CONTRIBUTING.md

@@ -24,6 +24,7 @@ had several contributions accepted, commit privileges are often quickly granted.
 * [What happens after submitting contribution?](#what-happens-after-submitting-contribution)
 * [What happens when your contribution is applied?](#what-happens-when-your-contribution-is-applied)
 * [Git commit rules](#git-commit-rules)
+* [Copyright and license headers](#copyright-and-license-headers)
 
 ## Pull requests
 
@@ -394,4 +395,28 @@ decreasing order under the fixed version.
 You can use [gitweb](https://git.php.net/) to look at PHP Git repository in
 various ways.
 
+## Copyright and license headers
+
+New source code files should include the following header block:
+
+```c
+/*
+  +----------------------------------------------------------------------+
+  | PHP Version 7                                                        |
+  +----------------------------------------------------------------------+
+  | Copyright (c) The PHP Group                                          |
+  +----------------------------------------------------------------------+
+  | This source file is subject to version 3.01 of the PHP license,      |
+  | that is bundled with this package in the file LICENSE, and is        |
+  | available through the world-wide-web at the following url:           |
+  | https://www.php.net/license/3_01.txt                                 |
+  | If you did not receive a copy of the PHP license and are unable to   |
+  | obtain it through the world-wide-web, please send a note to          |
+  | license@php.net so we can mail you a copy immediately.               |
+  +----------------------------------------------------------------------+
+  | Author:                                                              |
+  +----------------------------------------------------------------------+
+*/
+```
+
 Thank you for contributing to PHP!