update banner to reflect new official status (#128)

Author: bcumming

docs/index.md

@@ -1,3 +1,9 @@
+!!! info ""
+    This is the new CSCS documentation site, which replaces the [CSCS Knowledge Base](https://confluence.cscs.ch/display/KB).
+
+    The migration of old documentation is still not fully complete.
+    If you find documentation that is missing, please create a ticket on the documentation's [GitHub issue tracker](https://github.com/eth-cscs/cscs-docs/issues).
+
 # CSCS Documentation
 
 <div class="grid cards" markdown>

overrides/main.html

@@ -3,12 +3,12 @@
 {% block announce %}
 
 <p>
-Work in progress.
+This is the new CSCS documentation site, which replaces the <a href="https://confluence.cscs.ch/display/KB">CSCS Knowledge Base</a>.
 </p>
 
 <p>
-The information found here is up to date but incomplete. Many pages are still empty or missing.
-Please refer to <a href="https://docs.cscs.ch">docs.cscs.ch</a> for documentation missing from this site for the time being.
+The migration of old documentation is still not fully complete.
+If you find documentation that is missing, please create a ticket on the documentation's <a href="https://github.com/eth-cscs/cscs-docs/issues">GitHub issue tracker</a>.
 </p>
 
 {% endblock %}