Add link to Linux Guide and Hints

- signed-off-by: Tommy Nguyen <remyabel@gmail.com>

README.md

@@ -374,6 +374,12 @@ performance of any of your sites from across the globe.<br>
 &nbsp;&nbsp;:small_orange_diamond: <a href="http://pubs.opengroup.org/onlinepubs/9699919799/utilities/contents.html"><b>Shell & Utilities</b></a> - describes the commands and utilities offered to application programs by POSIX-conformant systems.<br>
 </p>
 
+##### :black_small_square: Linux
+
+<p>
+&nbsp;&nbsp;:small_orange_diamond: <a href="https://linuxguideandhints.com/"><b>Linux Guide and Hints</b></a> - tutorials on system administration in Fedora® and CentOS®, including OpenLDAP and FreeIPA.<br>
+</p>
+
 ##### :black_small_square: Programming
 
 <p>