Add Discussions (#212)

Add discussion in navigation bar

Author: arnavk23

_layout/navbar.html

@@ -53,6 +53,13 @@
     </div>
 
     <div class="navbar-end">
+      <a class="navbar-item icon-text" href="https://github.com/orgs/JuliaSmoothOptimizers/discussions">
+        <span class="icon">
+          <ion-icon size="large" name="chatbubbles-outline"></ion-icon>
+        </span>
+        <span>Discussions</span>
+      </a>
+
       <a class="navbar-item icon-text" href="https://github.com/JuliaSmoothOptimizers/juliasmoothoptimizers.github.io/issues">
         <span class="icon">
           <ion-icon size="large" name="logo-github"></ion-icon>