docs: add commments to core::Tracker struct fields

src/core/mod.rs

@@ -483,13 +483,24 @@ use crate::CurrentClock;
 pub struct Tracker {
     // The tracker configuration.
     config: Core,
+
     /// A database driver implementation: [`Sqlite3`](crate::core::databases::sqlite)
     /// or [`MySQL`](crate::core::databases::mysql)
     database: Arc<Box<dyn Database>>,
+
+    /// Tracker users' keys. Only for private trackers.
     keys: tokio::sync::RwLock<std::collections::HashMap<Key, auth::ExpiringKey>>,
+
+    /// The list of allowed torrents. Only for listed trackers.
     whitelist: tokio::sync::RwLock<std::collections::HashSet<InfoHash>>,
+
+    /// The in-memory torrents repository.
     torrents: Arc<Torrents>,
+
+    /// Service to send stats events.
     stats_event_sender: Option<Box<dyn statistics::EventSender>>,
+
+    /// The in-memory stats repo.
     stats_repository: statistics::Repo,
 }