Update README.md

A link to the HTTP response header database.

README.md

@@ -629,7 +629,7 @@ performance of any of your sites from across the globe.<br>
 &nbsp;&nbsp;:small_orange_diamond: <a href="http://www.insecam.org/"><b>Insecam</b></a> - the world biggest directory of online surveillance security cameras.<br>
 &nbsp;&nbsp;:small_orange_diamond: <a href="http://index-of.es/"><b>index-of</b></a> - contains great stuff like: security, hacking, reverse engineering, cryptography, programming etc.<br>
 &nbsp;&nbsp;:small_orange_diamond: <a href="https://opendata.rapid7.com/"><b>Rapid7 Labs Open Data</b></a> - is a great resources of datasets from Project Sonar.<br>
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+&nbsp;&nbsp;:small_orange_diamond: <a href="https://webtechsurvey.com/common-response-headers"><b>WebTechSurvey</b></a> - the largest database of HTTP response headers and websites using them.<br>
 </p>
 
 ##### :black_small_square: Generators