Add the README image to the common file types lesson

Describe the Issue

The common file types lesson is missing the README image included in its original transcript. The current lesson links to freeCodeCamp's README instead of displaying the image.

Lesson file: curriculum/challenges/english/blocks/lecture-working-with-file-systems/672ac403a9ba7732b31c6480.md.

The image is being added in https://github.com/freeCodeCamp/cdn/pull/409 and needs to be available on the CDN first. This is blocked by https://github.com/freeCodeCamp/cdn/pull/409.

For reference, the image appeared immediately after this paragraph in the original transcript:

They are usually written in a file format called Markdown. With Markdown, you can create structured documents with headings, subheadings, links, images, lists, and more. Markdown files have a .md or .markdown extension.

https://cdn.freecodecamp.org/curriculum/lecture-transcripts/what-are-some-common-file-types-you-will-work-with-in-web-applications-1.png

The original placement is a reference point. The contributor can choose a suitable placement for the current lesson and write descriptive alt text.

Affected Page

https://www.freecodecamp.org/learn/full-stack-developer/lecture-working-with-file-systems/what-are-some-common-file-types-you-will-work-with-in-web-applications

Expected behavior

The lesson includes the README image alongside the Markdown explanation, with descriptive alt text.