add 'knock'

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

README.md

@@ -159,6 +159,7 @@ Only main chapters:
 &nbsp;&nbsp;:small_orange_diamond: <a href="https://github.com/aboul3la/Sublist3r"><b>sublist3r</b></a> - is a fast subdomains enumeration tool for penetration testers.<br>
 &nbsp;&nbsp;:small_orange_diamond: <a href="https://github.com/OWASP/Amass"><b>amass</b></a> - is tool that obtains subdomain names by scraping data sources, crawling web archives and more.<br>
 &nbsp;&nbsp;:small_orange_diamond: <a href="https://github.com/google/namebench"><b>namebench</b></a> - provides personalized DNS server recommendations based on your browsing history.<br>
+&nbsp;&nbsp;:small_orange_diamond: <a href="https://github.com/guelfoweb/knock"><b>knock</b></a> - is a tool to enumerate subdomains on a target domain through a wordlist.<br>
 &nbsp;&nbsp;:small_orange_diamond: <a href="https://github.com/jedisct1/dnscrypt-proxy"><b>dnscrypt-proxy 2</b></a> - a flexible DNS proxy, with support for encrypted DNS protocols.<br>
 </p>