Add comment about rust-version field to Cargo.toml

Author: taiki-e

Cargo.toml

@@ -2,6 +2,7 @@
 name = "pin-project-lite"
 version = "0.2.16" #publish:version
 edition = "2018"
+# NB: Sync with rust-version field in other Cargo.toml files, msrv badge in README.md, and test job in .github/workflows/ci.yml
 rust-version = "1.37" # For underscore consts
 license = "Apache-2.0 OR MIT"
 repository = "https://github.com/taiki-e/pin-project-lite"