docs: add doccomment for get_courses

src/libcanvas/courses.rs

@@ -4,6 +4,7 @@ use time::serde::iso8601;
 use time::OffsetDateTime;
 
 impl CanvasClient {
+    /// Get a list of courses the current user is enrolled in.
     pub async fn get_courses(&self) -> Result<Vec<Course>, reqwest::Error> {
         let response = self
             .client