add filler as first project

project_urls.py

diff --git a/project_urls.py b/project_urls.py
index 5d00fd1..0bcff2b 100644
--- a/project_urls.py
+++ b/project_urls.py
@@ -1,5 +1,6 @@
 # name must be valid verilog module name set in scan_wrapper.v
 urls = [
+            'https://github.com/mattvenn/wokwi_filler',
             'https://github.com/mattvenn/wokwi-verilog-gds-test',
             'https://github.com/mattvenn/animation_tinytapeout_demo',
             'https://github.com/mattvenn/wokwi_inverters',