fix 2.6 first steps

Author: thboileau

content/documentation/user-guide/2.6/introduction/first-steps/overview.md

@@ -4,6 +4,6 @@ weight: 1
 ---
 This section will give you a first taste of the Restlet Framework:
 
-- [First server](./first-server "First server")
-- [First client](./first-client "First client")
-- [First application](./first-application "First application")
+- [First server](../first-server "First server")
+- [First client](../first-client "First client")
+- [First application](../first-application "First application")