Add readme, homepage and repo to Cargo.toml.

Cargo.toml

@@ -5,6 +5,9 @@ authors = ["Jing Yang <ditsing@gmail.com>"]
 description = "A RPC framework for testing"
 edition = "2018"
 license = "MIT"
+readme = "README.md"
+repository = "https://github.com/ditsing/labrpc"
+homepage = "https://github.com/ditsing/labrpc"
 
 [dependencies]
 bytes = "1.0"