Fix gitignore in template to only ignore root app directory

[windsnow1025]

Summary

This PR addresses an issue with the .gitignore file generated by the npx create-nextron-app command. The current configuration ignores all directories named app throughout the project, which can lead to unintended ignoring of important files in nested directories. This PR modifies the .gitignore configuration to only ignore the app directory at the root of the project.

Changes

• Updated the .gitignore entry from app to /app in the examples/_template/gitignore.txt file.

Issue

Fixes #452

[saltyshiomix]

@windsnow1025

I just published nextron v9.1.0, which includes your PR 🎉