Improve documentation for PayloadConfig (#1923)

src/types/payload.rs

@@ -191,22 +191,25 @@ fn bytes_to_string(body: Bytes, encoding: &'static Encoding) -> Result<String, E
 /// building extractors on top of `Payload`.
 ///
 /// By default, the payload size limit is 256kB and there is no mime type condition.
+///
+/// To use this, add an instance of it to your app or service through one of the
+/// `.app_data()` methods.
 #[derive(Clone)]
 pub struct PayloadConfig {
     limit: usize,
     mimetype: Option<Mime>,
 }
 
 impl PayloadConfig {
-    /// Create new instance with a size limit and no mime type condition.
+    /// Create new instance with a size limit (in bytes) and no mime type condition.
     pub fn new(limit: usize) -> Self {
         Self {
             limit,
             ..Default::default()
         }
     }
 
-    /// Set maximum accepted payload size. The default limit is 256kB.
+    /// Set maximum accepted payload size in bytes. The default limit is 256kB.
     pub fn limit(mut self, limit: usize) -> Self {
         self.limit = limit;
         self