added 'Labs' chapter

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

README.md

@@ -303,6 +303,12 @@ Linux Security Expert</b></a> - trainings, howtos, checklists, security tools an
 &nbsp;&nbsp;:small_orange_diamond: <a href="https://github.com/opendns/Security_Ninjas_AppSec_Training"><b>Security Ninjas</b></a> - open source application security training program.<br>
 </p>
 
+##### :black_small_square: Labs
+
+<p>
+&nbsp;&nbsp;:small_orange_diamond: <a href="https://www.hackthebox.eu/"><b>Hack The Box</b></a> - online platform allowing you to test your penetration testing skills.<br>
+</p>
+
 #### One-liners
 
 ##### Table of Contents