Add some docs

src/middleware/logger.rs

@@ -126,6 +126,8 @@ impl Logger {
         self
     }
 
+    /// Register a closure to be run on the logger. 
+    /// Note: output from closure will be present at end of logger output. Multiple closure will be ran in the order they are registed.
     pub fn register_closure(
         mut self,
         closure: fn(req: &ServiceRequest) -> String,