Required PHP version header (#238)

Required PHP version header

Author: schlessera

templates/plugin-readme.mustache

@@ -4,6 +4,7 @@ Donate link: https://example.com/
 Tags: comments, spam
 Requires at least: 4.5
 Tested up to: {{plugin_tested_up_to}}
+Requires PHP: 5.6
 Stable tag: 0.1.0
 License: GPLv2 or later
 License URI: https://www.gnu.org/licenses/gpl-2.0.html