Added nmon to system diagnostics

README.md

@@ -326,6 +326,7 @@ Only main chapters:
 &nbsp;&nbsp;:small_orange_diamond: <a href="https://github.com/mozilla/rr"><b>rr</b></a> - is a lightweight tool for recording, replaying and debugging execution of applications.<br>
 &nbsp;&nbsp;:small_orange_diamond: <a href="https://pcp.io/index.html"><b>Performance Co-Pilot</b></a> - a system performance analysis toolkit.</br>
 &nbsp;&nbsp;:small_orange_diamond: <a href="https://github.com/sharkdp/hexyl"><b>hexyl</b></a> - a command-line hex viewer.<br>
+&nbsp;&nbsp;:small_orange_diamond: <a href="http://nmon.sourceforge.net/pmwiki.php"><b>nmon</b></a> - a single executable for performance monitoring and data analysis.<br>
 </p>
 
 ##### :black_small_square: Log Analyzers