Change summary

This PR adjusts the broken link in Welcome Guide, in sectionGet Started Tutorials.

Adjusted URL in content/docs/welcome-guide/_index.md:

From:
[Create your first game: Pong!](/docs/learning-guide/tutorials/first-project/)

To:
[Create your first game: Pong!](/docs/learning-guide/samples/follow-along/pong/)

• I checked if the URL existed elsewhere in the code, but I couldn't find it.
• I checked another open PR, but the link is with ".md", which is not necessary.

If it is not useful, you can close it.

Submission Checklist:

• Descriptive active voice - Do descriptive sentences have a clear subject and action verb?
• Answer the question at hand - Does the documentation answer a what, why, how, or where type of question?
• Consistency - Does the content consistently follow the Style Guide?
• Help the user - Does the documentation show the user something meaningful?