feat: add images for color theory lesson

[majestic-owl448]

Checklist:

• I have read freeCodeCamp's contribution guidelines.
• My pull request has a descriptive title (not a vague title like Update index.md)

Closes #328

I don't know if this is the best idea for the attributions, but I don't know how else, and I did not receive response

[jdwilkin4]

It looks like that should work. I will bring it up on the huddle just to confirm so we can get a definitive answer 👍🏾

[jdwilkin4]

@QuincyLarson

Here is the full context.

We are adding images to the this lesson block here on the site

https://www.freecodecamp.org/learn/responsive-web-design-v9/#lecture-working-with-colors-in-css

These images were included in the original video form of the lessons but they were removed when we just went with the text only format.

We need to know the right way to attribute these images. We tried to find ways to create these images ourselves but that wasn't feasible. These images come from wikipedia and should be creative commons but it looks like some of them aren't. So we need to know if the attribution file ilenia added will work.

[QuincyLarson]

If the person who created the video also created the graphics, we can just say:

"Image Credit: [author @ handle] on YouTube" under the images and leave it at that.

Otherwise, we may want to just create our own version of these images. It's hard to tell without seeing the exact images you're planning to add. If they're CC0 or public domain images, no attribution is necessary.

[jdwilkin4]

I went ahead and created a separate issue for creating the new illustrations.
#345

We will find someone on the team to create those.
As for this PR, let's delete the attributions file and the related three images that cannot be used.

Then this PR can be approved and merged in 👍🏾