Add some documentation

src/api.rs

@@ -1,16 +1,20 @@
+//! Low-level client for interacting with the [Toggl API](https://developers.track.toggl.com/docs/).
+
 use chrono::NaiveDate;
 use reqwest::header;
 use serde::{Deserialize, Serialize};
 use serde_json::Number;
 
 static BASE_API_URL: &str = "https://api.track.toggl.com/api/v9";
 
+/// Low-level client for interacting with the [Toggl API](https://developers.track.toggl.com/docs/).
 pub struct Client {
     c: reqwest::blocking::Client,
     token: String,
 }
 
 impl Client {
+    /// Creates a new client with the given API token.
     pub fn new(token: String) -> Result<Self, reqwest::Error> {
         let mut headers = header::HeaderMap::new();
 

src/error.rs

@@ -1,9 +1,13 @@
+//! Defines the error type for top-level CLI commands.
+
+/// Error type for top-level CLI commands.
 #[derive(Debug)]
 pub struct Error {
     pub message: String,
 }
 
 impl Error {
+    /// Creates a new entry with the given message.
     pub fn new(message: String) -> Self {
         Self { message }
     }

src/svc.rs

@@ -1,3 +1,5 @@
+//! High-level client for interacting with Toggl. Uses the [api].
+
 use crate::api;
 use chrono::{DateTime, Duration, TimeZone, Utc};