Added conditionals to swap video and add a disclaimer on first lesson

[intelagense]

Description

I've implemented conditional statements to check for the missing video ID. When a match is found, the video is swapped, and a brief disclaimer is added.

This method, while differing from the initial suggestion in #31, I believe, minimizes user confusion by keeping them on the same page, rather than redirecting them to a new page or YouTube.

This approach is not only straightforward to reverse or modify in the future but also was more manageable to implement without needing extensive knowledge of pug.js.

Please let me know if this solution is acceptable, or if I should instead proceed with adding a separate route and page as initially proposed.

Closes #31

[labrocadabro]

Works for me, can you just do two things:

1) In the disclaimer add a "more info" link that goes to Leon's twitter message.

2) Change the title of this PR so that it's linked to the issue. Just add closes #31 and that should do it.

https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue

[intelagense]

I stumbled on a typo, but the link has been added and it looks like it is properly linked now through the last commit message.

[labrocadabro]

I didn't want to quibble about the issue linking as it wasn't that important. But for future reference, you have to put it in the title rather than the description.

[labrocadabro]

Oh uh never mind, apparently the description works too haha.

[20jasper]

@intelagense LET"S GOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO

(commenting since I saw it on my github homepage haha)