doc: Update index.mdx with links to core concepts documentation

Author: CarLeonDev

Diff for: website/src/content/docs/index.mdx

@@ -47,6 +47,7 @@ import ScriptIndex from "@/components/ScriptIndex.astro";
   <Card title="Fine-grained reactivity" icon="rocket">
     React to changes at the finest level of granularity, providing precise
     control and responsiveness in your app.
+    Learn more about [Rendering control](/reactter/core_concepts/rendering_control).
   </Card>
   <Card title="Lightweight" icon="telegram">
     Reactter boasts a minimal footprint, ensuring efficient performance without
@@ -60,8 +61,8 @@ import ScriptIndex from "@/components/ScriptIndex.astro";
     configurations.
   </Card>
   <Card title="Highly reusable" icon="seti:json">
-    Share states and logic across your app using Custom Hooks and Dependency
-    Injection.
+    Share states and logic across your app using [Dependency
+    Injection](/reactter/core_concepts/dependency_injection) and [Custom Hooks](/reactter/core_concepts/hooks/#custom-hook).
   </Card>
   <Card title="100% Dart" icon="seti:dart">
     Supports Dart server, Dart JS (HTML), Flutter (Web, Mobile and Desktop),
@@ -70,6 +71,8 @@ import ScriptIndex from "@/components/ScriptIndex.astro";
   </Card>
   <Card title="Fully testable" icon="approve-check">
     Test your states and logic easily. Reactter is 100% test coverage.
+
+    [![Codecov](https://img.shields.io/codecov/c/github/2devs-team/reactter?logo=codecov)](https://app.codecov.io/gh/2devs-team/reactter)
   </Card>
 </CardGrid>