Minor: comment in Cargo.toml about MSRV (apache#14809)

- I wasn't able to quickly find where the MSRV was defined when filing  apache#14808 so I would like to make it easier to find nex time

Author: alamb

Cargo.toml

@@ -66,7 +66,9 @@ homepage = "https://datafusion.apache.org"
 license = "Apache-2.0"
 readme = "README.md"
 repository = "https://github.com/apache/datafusion"
+# Define Minimum Supported Rust Version (MSRV)
 rust-version = "1.82.0"
+# Define DataFusion version
 version = "45.0.0"
 
 [workspace.dependencies]