Update READMEs for the JavaScript Fundamentals rename (#1474)

The top-level README still welcomed trainees to the Onboarding module and
had no curriculum link. The Sprint 2 prep link was missing /itp/ and 404'd,
and the Sprint 3 guide was titled "week 2".

Co-authored-by: Abdi Saeed <abdi.saeed2009@gmail.com>

Author: abdishakoor-dev

Sprint-2/README.md

@@ -1,6 +1,6 @@
 # 🧭 Guide to Sprint 2 exercises
 
-> https://curriculum.codeyourfuture.io/javascript-fundamentals/sprints/2/prep/
+> https://curriculum.codeyourfuture.io/itp/javascript-fundamentals/sprints/2/prep/
 
 > [!TIP]
 > You should always do the prep work _before_ attempting the coursework.

Sprint-3/README.md

@@ -1,4 +1,4 @@
-# 🧭 Guide to week 2 exercises
+# 🧭 Guide to Sprint 3 exercises
 
 > https://curriculum.codeyourfuture.io/itp/javascript-fundamentals/sprints/3/prep/
 

readme.md

@@ -1,4 +1,6 @@
-# 🤝 Welcome to your Onboarding Module
+# 🤝 Welcome to your JavaScript Fundamentals Module
+
+> https://curriculum.codeyourfuture.io/itp/javascript-fundamentals/
 
 ## 🔑 Do the prep