Update Readme docs

Author: leonelquinteros

README.md

@@ -283,6 +283,56 @@ y.UseCache = false
 ```
 
 
+### Chain and extend
+
+Just use the Yarf object as any http.Handler on a chain. 
+Set another http.Handler on the Yarf.Follow property to be followed in case this Yarf router can't match the request. 
+
+Here's an example on how to follow the request to a public file server: 
+
+```go
+package main 
+
+import (
+    "github.com/yarf-framework/yarf"
+    "net/http"
+)
+
+func main() {
+    y := yarf.New()
+
+    // Add some routes
+    y.Add("/hello/:name", new(Hello))
+    
+    //... more routes here
+    
+    // Follow to file server
+    y.Follow = http.FileServer(http.Dir("/var/www/public"))
+    
+    // Start the server
+    y.Start(":8080")
+}
+```
+
+
+### Custom NotFound error handler
+
+You can handle all 404 errors returned by any resource/middleware during the request flow of a Yarf server. 
+To do so, you only have to implement a function with the func(c *yarf.Context) signature and set it to your server's Yarf.NotFound property.
+
+```go
+y := yarf.New()
+
+// ...
+
+y.NotFound = func(c *yarf.Context) {
+    c.Render("This is a custom Not Found handler")
+}
+
+// ...
+``` 
+
+
 ## Performance
 
 On initial benchmarks, the framework seems to perform very well compared with other similar frameworks. 
@@ -338,37 +388,6 @@ func main() {
 
 ```
 
-## Chain and extend
-
-Just use the Yarf object as any http.Handler on a chain. 
-Set another http.Handler on the Yarf.Follow property to be followed in case this Yarf router can't match the request. 
-
-Here's an example on how to follow the request to a public file server: 
-
-```go
-package main 
-
-import (
-    "github.com/yarf-framework/yarf"
-    "net/http"
-)
-
-func main() {
-    y := yarf.New()
-
-    // Add some routes
-    y.Add("/hello/:name", new(Hello))
-    
-    //... more routes here
-    
-    // Follow to file server
-    y.Follow = http.FileServer(http.Dir("/var/www/public"))
-    
-    // Start the server
-    y.Start(":8080")
-}
-```
-
 
 ## Why another micro-framework? 
 

yarf.go

@@ -37,7 +37,7 @@ type Yarf struct {
 	// Follow defines a standard http.Handler implementation to follow if no route matches.
 	Follow http.Handler
 
-	// NotFound defines a function interface to execute when a NotFound error is thrown.
+	// NotFound defines a function interface to execute when a NotFound (404) error is thrown.
 	NotFound func(c *Context)
 }