Adding instructions to generate .proto files

Change-Id: I82670f2f5a44e662ac24ca4cf55b6118fe7e0f27
diff --git a/SUMMARY.md b/SUMMARY.md
index ba8f447..4c668a6 100644
--- a/SUMMARY.md
+++ b/SUMMARY.md
@@ -66,6 +66,7 @@
         * [Core Models](xos/core_models.md)
         * [Security Policies](xos/security_policies.md)
         * [Tutorial](xos/tutorials/basic_synchronizer.md)
+        * [Build proto files from xProto](xos/dev/xproto_to_protobuf.md)
     * [Developer Workflows](developer/workflows.md)
         * [Working on R-CORD Without an OLT/ONU](developer/configuration_rcord.md)
     * [Building Docker Images](developer/imagebuilder.md)