Merge #290: Crate docs for primitives package

f78638a docs: [#279] crate docs for locate-error package (Jose Celano)

Pull request description:

  Documentation for the `primitives` package (`./package/primitives`).

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Tree-SHA512: 1daff76f3acdc41df21916232c785c60a359a556867a03fe363377b9880cfd13c3668d7ec192b5fa698e4c5da83eb9c85c7decf086c7322c928ab20716ddfe7a

Author: josecelano

packages/primitives/src/lib.rs

@@ -1,27 +1,47 @@
+//! Primitive types for [Torrust Tracker](https://docs.rs/torrust-tracker).
+//!
+//! This module contains the basic data structures for the [Torrust Tracker](https://docs.rs/torrust-tracker),
+//! which is a `BitTorrent` tracker server. These structures are used not only
+//! by the tracker server crate, but also by other crates in the Torrust
+//! ecosystem.
 use serde::{Deserialize, Serialize};
 
-// TODO: Move to the database crate once that gets its own crate.
+/// The database management system used by the tracker.
+///
+/// Refer to:
+///
+/// - [Torrust Tracker Configuration](https://docs.rs/torrust-tracker-configuration).
+/// - [Torrust Tracker](https://docs.rs/torrust-tracker).
+///
+/// For more information about persistence.
 #[derive(Serialize, Deserialize, PartialEq, Eq, Debug, derive_more::Display, Clone)]
 pub enum DatabaseDriver {
+    // TODO: Move to the database crate once that gets its own crate.
+    /// The Sqlite3 database driver.
     Sqlite3,
+    /// The MySQL database driver.
     MySQL,
 }
 
+/// The mode the tracker will run in.
+///
+/// Refer to [Torrust Tracker Configuration](https://docs.rs/torrust-tracker-configuration)
+/// to know how to configure the tracker to run in each mode.
 #[derive(Serialize, Deserialize, Copy, Clone, PartialEq, Eq, Debug)]
 pub enum TrackerMode {
-    // Will track every new info hash and serve every peer.
+    /// Will track every new info hash and serve every peer.
     #[serde(rename = "public")]
     Public,
 
-    // Will only track whitelisted info hashes.
+    /// Will only track whitelisted info hashes.
     #[serde(rename = "listed")]
     Listed,
 
-    // Will only serve authenticated peers
+    /// Will only serve authenticated peers
     #[serde(rename = "private")]
     Private,
 
-    // Will only track whitelisted info hashes and serve authenticated peers
+    /// Will only track whitelisted info hashes and serve authenticated peers
     #[serde(rename = "private_listed")]
     PrivateListed,
 }