Use "scheme" term over "protocol" in links-and-images.md

[martineau-sw]

Opt to use scheme over protocol in Links and Images course to infer broader use cases of absolute links based on reading found in "How Does the Web Work?" course. Specific article is a prerequisite reading of DNS reading and directly linked as a refresher.

Because

Prefer the term "scheme" over "protocol" based on What is a URL? MDN article and Introduction to HTTP book within How Does the Web Work? to infer broader use cases of absolute links to new web developers.

This PR

• Change "protocol" occurrences to "scheme" within the lesson
• Inline link to MDN article about structure of URL as a refresher and more information

Additional Information

Root Discord message of reply thread between marti (myself) and Mao && "Don't rush learning!"

Pull Request Requirements

• [x] I have thoroughly read and understand The Odin Project curriculum contributing guide
• [x] The title of this PR follows the location of change: brief description of change format, e.g. Intro to HTML and CSS lesson: Fix link text
• [x] The Because section summarizes the reason for this PR
• [x] The This PR section has a bullet point list describing the changes in this PR
• [x] If this PR addresses an open issue, it is linked in the Issue section
• [x] If any lesson files are included in this PR, they have been previewed with the Markdown preview tool to ensure it is formatted correctly
• [x] If any lesson files are included in this PR, they follow the Layout Style Guide