add dependency

Cargo.toml

@@ -34,6 +34,7 @@ default = [
   "mio-uds",
   "num_cpus",
   "pin-project-lite",
+  "smol",
 ]
 docs = ["attributes", "unstable", "default"]
 unstable = ["std", "broadcaster", "futures-timer"]
@@ -74,6 +75,7 @@ once_cell = { version = "1.3.1", optional = true }
 pin-project-lite = { version = "0.1.4", optional = true }
 pin-utils = { version = "0.1.0-alpha.4", optional = true }
 slab = { version = "0.4.2", optional = true }
+smol = { path = "../smol", optional = true }
 
 [dev-dependencies]
 femme = "1.3.0"