Add docc comment about middleware application (#745)

Author: adam-fowler

Sources/Hummingbird/Router/RouteCollection.swift

@@ -40,6 +40,9 @@ public final class RouteCollection<Context: RequestContext>: RouterMethods {
     }
 
     /// Add middleware to RouteCollection
+    ///
+    /// This middleware will only be applied to endpoints added after this call.
+    /// - Parameter middleware: Middleware we are adding
     @discardableResult public func add(middleware: any MiddlewareProtocol<Request, Response, Context>) -> Self {
         self.middlewares.add(middleware)
         return self

Sources/Hummingbird/Router/RouterGroup.swift

@@ -41,6 +41,9 @@ public struct RouterGroup<Context: RequestContext>: RouterMethods {
     }
 
     /// Add middleware to RouterGroup
+    ///
+    /// This middleware will only be applied to endpoints added after this call.
+    /// - Parameter middleware: Middleware we are adding
     @discardableResult public func add(middleware: any MiddlewareProtocol<Request, Response, Context>) -> RouterGroup<Context> {
         self.middlewares.add(middleware)
         return self

Sources/Hummingbird/Router/RouterMethods.swift

@@ -34,6 +34,9 @@ public protocol RouterMethods<Context>: _HB_SendableMetatype {
     ) -> Self where Responder.Context == Context
 
     /// add middleware
+    ///
+    /// This middleware will only be applied to endpoints added after this call.
+    /// - Parameter middleware: Middleware we are adding
     func add(middleware: any MiddlewareProtocol<Request, Response, Context>) -> Self
 }
 
@@ -123,6 +126,8 @@ extension RouterMethods {
     /// ```
     /// This gives a slight performance boost over adding them individually.
     ///
+    /// The middleware will only be applied to endpoints added after this call.
+    ///
     /// - Parameter buildMiddlewareStack: Middleware stack result builder
     /// - Returns: router
     @discardableResult public func addMiddleware(