docs: update section titles and remove redundant content in iApp guide

- Renamed the section "Launch your iApp" to "Build your iApp" for clarity.
- Removed the redundant "Update your iApp" subsection to streamline the documentation.

Author: Le-Caignec

src/references/iapp-generator/building-your-iexec-app.md

@@ -84,7 +84,7 @@ You'll set up:
 For more details and to learn how to use them in your application, refer here
 [Inputs and Outputs](/guides/build-iapp/inputs-and-outputs)
 
-## 🚀 Launch your iApp
+## 🚀 Build your iApp
 
 After initialization, the following essential files and directories are
 generated:
@@ -97,8 +97,6 @@ generated:
   - `output/`
   - `cache/`
 
-### 📝 Update your iApp
-
 To modify your main application logic open:
 
 ```sh