Give more context on feed exceptions

src/main.rs

@@ -36,8 +36,16 @@ struct FeedItem {
 }
 
 fn fetch_feed(url: impl IntoUrl) -> Result<Feed> {
-    let content = reqwest::blocking::get(url)?.bytes()?;
-    Ok(parse(&content[..])?)
+    let r = reqwest::blocking::get(url)
+        .context("Failed to fetch feed")?;
+
+    let content = r.bytes()
+        .context("Failed to read feed contents")?;
+
+    let feed = parse(&content[..])
+        .context("Failed to parse feed")?;
+
+    Ok(feed)
 }
 
 struct FeedFile {