Update community section: combine forum and mailing list, add general description

Author: shinaoka

index.md

@@ -2,19 +2,24 @@
 
 This website collects information from the tensor4all group which is working on tensor network methods based on tensor cross interpolation (TCI) and related tensor learning algorithms such as quantics/quantized tensor trains.
 
-## News
+## Join our community!
 
 <div style="background-color: #e8f4fd; border: 2px solid #2196F3; border-radius: 8px; padding: 20px; margin: 20px 0; text-align: center; box-shadow: 0 2px 4px rgba(0,0,0,0.1);">
-  <h3 style="color: #1976D2; margin-top: 0; font-size: 1.4em;">🎉 New Forum Available!</h3>
-  <p style="font-size: 1.2em; margin: 10px 0; font-weight: 500;">
-    The <a href="https://tensor4all.discourse.group" style="color: #1976D2; text-decoration: none; font-weight: bold;">tensor4all discourse forum</a> is now open!
+  <h3 style="color: #1976D2; margin-top: 0; font-size: 1.4em;">🤝 Join our community!</h3>
+  <p style="font-size: 1.1em; margin: 15px 0; color: #424242;">
+    Connect with researchers working on tensor networks and related methods. Join our <a href="https://tensor4all.discourse.group" style="color: #1976D2; text-decoration: none; font-weight: bold;">Discourse forum</a> for discussions, or subscribe to our <a href="https://groups.google.com/g/tensor4all" style="color: #1976D2; text-decoration: none; font-weight: bold;">Google Groups mailing list</a> for meeting announcements.
   </p>
-  <p style="margin: 10px 0; color: #424242;">
-Please feel free to ask questions and discuss your ideas with us.
+  <p style="font-size: 0.9em; margin: 10px 0; color: #666;">
+    Don't have a Google account? Contact us at <a href="mailto:tensor4all-admin@googlegroups.com" style="color: #1976D2; text-decoration: none;">tensor4all-admin@googlegroups.com</a> to join the mailing list.
   </p>
-  <a href="https://tensor4all.discourse.group" style="display: inline-block; background-color: #2196F3; color: white; padding: 12px 24px; text-decoration: none; border-radius: 6px; font-weight: bold; margin-top: 10px; transition: background-color 0.3s;" onmouseover="this.style.backgroundColor='#1976D2'" onmouseout="this.style.backgroundColor='#2196F3'">
-    Join the Discussion →
-  </a>
+  <div style="display: flex; gap: 15px; justify-content: center; flex-wrap: wrap; margin-top: 15px;">
+    <a href="https://tensor4all.discourse.group" style="display: inline-block; background-color: #2196F3; color: white; padding: 12px 24px; text-decoration: none; border-radius: 6px; font-weight: bold; transition: background-color 0.3s;" onmouseover="this.style.backgroundColor='#1976D2'" onmouseout="this.style.backgroundColor='#2196F3'">
+      Join Forum →
+    </a>
+    <a href="https://groups.google.com/g/tensor4all" style="display: inline-block; background-color: white; color: #2196F3; padding: 12px 24px; text-decoration: none; border-radius: 6px; font-weight: bold; border: 2px solid #2196F3; transition: background-color 0.3s;" onmouseover="this.style.backgroundColor='#e8f4fd'" onmouseout="this.style.backgroundColor='white'">
+      Join Mailing List →
+    </a>
+  </div>
 </div>
 
 ## Literature