Updating the index file for design proposals

--
MOS_MIGRATED_REVID=129432777
diff --git a/site/designs/index.md b/site/designs/index.md
index c9cc8cd..9965d2b 100644
--- a/site/designs/index.md
+++ b/site/designs/index.md
@@ -20,3 +20,4 @@
 through the [Skylark Design Process](/designs/skylark-design-process.html).
 
 1. [Parameterized Skylark Aspects](/designs/skylark-parameterized-aspects.html).
+2. [Declared Providers](/designs/declared-providers.html).