update 404.rst

Author: acharraggi

docs/source/404.rst

@@ -6,7 +6,8 @@
 Page not found
 ==============
 
-Unfortunately we couldn't find the content you were looking for.
+Unfortunately we couldn't find the content you were looking for. Try using the sidebar menu links or search box.
+
+TensorFlow and the *FIRST* Machine Learning Toolchain content has been moved to the `FTC Docs Archive <https://ftc-docs.firstinspires.org/projects/ftcdocs-archive/en/latest/index.html>`__.
 
-Possibly the content was moved to the `FTC Docs Archive <https://ftc-docs.firstinspires.org/projects/ftcdocs-archive/en/latest/index.html>`__.