Add notice on upgrading some constants (#4532)

Co-authored-by: Andronik Ordian <write@reusable.software>

polkadot/primitives/src/v1/mod.rs

@@ -241,6 +241,7 @@ pub const ASSIGNMENT_KEY_TYPE_ID: KeyTypeId = KeyTypeId(*b"asgn");
 /// * initial genesis for the Parachains configuration
 /// * checking updates to this stored runtime configuration do not exceed this limit
 /// * when detecting a code decompression bomb in the client
+// NOTE: This value is used in the runtime so be careful when changing it.
 pub const MAX_CODE_SIZE: u32 = 3 * 1024 * 1024;
 
 /// Maximum head data size we support right now.
@@ -248,6 +249,7 @@ pub const MAX_CODE_SIZE: u32 = 3 * 1024 * 1024;
 /// Used for:
 /// * initial genesis for the Parachains configuration
 /// * checking updates to this stored runtime configuration do not exceed this limit
+// NOTE: This value is used in the runtime so be careful when changing it.
 pub const MAX_HEAD_DATA_SIZE: u32 = 1 * 1024 * 1024;
 
 /// Maximum PoV size we support right now.
@@ -256,6 +258,7 @@ pub const MAX_HEAD_DATA_SIZE: u32 = 1 * 1024 * 1024;
 /// * initial genesis for the Parachains configuration
 /// * checking updates to this stored runtime configuration do not exceed this limit
 /// * when detecting a PoV decompression bomb in the client
+// NOTE: This value is used in the runtime so be careful when changing it.
 pub const MAX_POV_SIZE: u32 = 5 * 1024 * 1024;
 
 // The public key of a keypair used by a validator for determining assignments