Add Est. 2015 with link to first commit in footer (#819)

* Initial plan

* Add Est. 2015 with link to first commit in footer

Co-authored-by: ckenst <6896787+ckenst@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: ckenst <6896787+ckenst@users.noreply.github.com>

Author: Copilot

_includes/footer.html

@@ -30,7 +30,7 @@
       </div>
     </div>
     <div class="footer-col-wrapper">
-      © 2025 Software Testing Conferences and Workshops
+      © 2025 Software Testing Conferences and Workshops | <a href="https://github.com/TestingConferences/testingconferences.github.io/commit/1b028cfba42af75900682818914203c2f87532a4">Est. 2015</a>
     </div>
     <div class="footer-col-wrapper">
       Are we missing anything? If so consider <a href="/how-to-contribute/">contributing</a>.