submodule: update handbook - add CONTRIBUTING with maintenance experience

Guo-Zhang · Guo-Zhang · commit 3a403ed152bf · 2026-04-08T21:05:59.000+08:00
diff --git a/docs/handbook b/docs/handbook
@@ -1 +1 @@
-Subproject commit 77c92f046ef9f8fcebf8f220becade9d62aa1ea0
+Subproject commit 6ad905496602b155ede88105ef504d33835e0348
