Add docs directory

docs/trailing-slash.md

@@ -0,0 +1,53 @@
+# trailing-slash middleware
+
+This middleware handles Trailing Slash in the URL on a GET request.
+
+`*append-trailing-slash*` redirects the URL to which it added the Trailing Slash if the content was not found. Also, `*trim-trailing-slash*` will remove the Trailing Slash.
+
+## Usage
+
+Example of redirecting a GET request of `/about/me` to `/about/me/`.
+
+```lisp
+(defpackage #:app/main
+  (:use #:cl)
+  (:import-from #:ningle)
+  (:import-from #:lack)
+  (:import-from #:lack-mw
+                #:*append-trailing-slash*))
+(in-package #:app/main)
+
+(defparameter *raw-app* (make-instance 'ningle:app))
+(setf (ningle:route *raw-app* "/about/me/")
+      "With Trailing Slash")
+
+(defparameter *app*
+  (lack:builder
+    *append-trailing-slash*
+    *raw-app*))
+```
+
+Example of redirecting a GET request of `/about/me/` to `/about/me`.
+
+```lisp
+(defpackage #:app/main
+  (:use #:cl)
+  (:import-from #:ningle)
+  (:import-from #:lack)
+  (:import-from #:lack-mw
+                #:*trim-trailing-slash*))
+(in-package #:app/main)
+
+(defparameter *raw-app* (make-instance 'ningle:app))
+(setf (ningle:route *raw-app* "/about/me")
+      "Without Trailing Slash")
+
+(defparameter *app*
+  (lack:builder
+    *trim-trailing-slash*
+    *raw-app*))
+```
+
+## Note
+
+It will be enabled when the request method is GET and the response status is `404`.