update Announcement block for 4.0.0

Author: deadbytefpv

overrides/main.html

@@ -13,5 +13,5 @@
 />
 {% endblock %}
 {% block announce %}
-ExpressLRS v3.6.3 is out now! Check it out on <a href="https://github.com/ExpressLRS/ExpressLRS/releases/tag/3.6.3">GitHub</a>.
+ExpressLRS v4.0 is out now! Check it out on <a href="https://github.com/ExpressLRS/ExpressLRS/releases/tag/4.0.0">GitHub</a>.
 {% endblock %}