added 'System hardening' chapter

- signed-off-by: trimstray <trimstray@gmail.com>

README.md

@@ -379,6 +379,13 @@ performance of any of your sites from across the globe.<br>
 &nbsp;&nbsp;:small_orange_diamond: <a href="http://cb.vu/unixtoolbox.xhtml"><b>Unix Toolbox</b></a> - collection of Unix/Linux/BSD commands and tasks which are useful for IT work or for advanced users.<br>
 </p>
 
+##### :black_small_square: System hardening
+
+<p>
+&nbsp;&nbsp;:small_orange_diamond: <a href="https://highon.coffee/blog/security-harden-centos-7/"><b>Security Harden CentOS 7</b></a> - this walks you through the steps required to security harden CentOS.<br>
+&nbsp;&nbsp;:small_orange_diamond: <a href="https://highon.coffee/blog/security-harden-centos-7/"><b>CentOS 7 Server Hardening Guide</b></a> - great guide for hardening CentOS; familiar with OpenSCAP.<br>
+</p>
+
 ##### :black_small_square: Security
 
 <p>