Include readme metadata in Cargo.toml
diff --git a/Cargo.toml b/Cargo.toml
index 37449d8..4e3122f 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,6 +7,7 @@
 repository = "https://github.com/dtolnay/syn"
 documentation = "https://docs.rs/syn"
 categories = ["development-tools::procedural-macro-helpers"]
+readme = "README.md"
 include = ["/Cargo.toml", "/src/**/*.rs", "/README.md", "/LICENSE-APACHE", "/LICENSE-MIT"]
 
 [[example]]