Add comment to capability exports

Author: chipshort

packages/std/src/exports.rs

@@ -29,6 +29,9 @@ use crate::serde::{from_json, to_json_vec};
 use crate::types::Env;
 use crate::{CustomMsg, Deps, DepsMut, MessageInfo};
 
+// These functions are used as markers for the chain to know which features this contract requires.
+// If the chain does not support all the required features, it will reject storing the contract.
+// See `docs/CAPABILITIES.md` for more details.
 #[cfg(feature = "iterator")]
 #[no_mangle]
 extern "C" fn requires_iterator() -> () {}