Enable issues in tvm-rfcs, so that RFCs can be tracked on roadmaps. (#56)

diff --git a/.asf.yaml b/.asf.yaml
index 8c85027..7316db2 100644
--- a/.asf.yaml
+++ b/.asf.yaml
@@ -17,6 +17,8 @@
 
 github:
   description: "A home for the final text of all TVM RFCs."
+  features:
+    issues: true  # Enable for roadmap tracking.
   labels:
     - tvm
     - vta