doc: add some comments for BEP 30 implementation

src/models/torrent_file.rs

@@ -216,6 +216,7 @@ impl TorrentInfoDictionary {
 
         // a torrent file has a root hash or a pieces key, but not both.
         if root_hash > 0 {
+            // If `root_hash` is true the `pieces` field contains the `root hash`
             info_dict.root_hash = Some(pieces.to_owned());
         } else {
             let buffer = into_bytes(pieces).expect("variable `torrent_info.pieces` is not a valid hex string");

src/services/torrent_file.rs

@@ -14,7 +14,7 @@ pub struct CreateTorrentRequest {
     pub pieces: String,
     pub piece_length: i64,
     pub private: Option<u8>,
-    pub root_hash: i64,
+    pub root_hash: i64, // True (1) if it's a BEP 30 torrent.
     pub files: Vec<TorrentFile>,
     // Other fields of the root level metainfo dictionary
     pub announce_urls: Vec<Vec<String>>,