[Practice Exercise Lint]: General Markdown Cleanup, Link Checks, Spelling, & Docs Sync.

[BethanyG]

Went through the practice exercises to check general Markdown formatting, links, and anything else that jumped out. Changes below:

• [x] Acronym (corrected table formatting)
• [x] Anagram (updated instructions.md from problem specs)
• [x] Armstrong Numbers (changed in-line link to a ref-link)
• [x] Atbash Cipher (corrected capitalization and one-sentence-per-line)
• [x] Binary (corrected one-sentence-per-line)
• [x] Bob (synced with problem specs instructions.md --> introduction.md & instructions.md)
• [x] Difference of Squares (corrected one-sentence-per-line)
• [x] Queen-attack: (corrected grammar on 2nd to last line.)
• [x] Simple-Linked-List (fixed chose --> choose typo)
• [x] Triangle (synced instructions.md to problem specs)

If any of these look hanky, happy to back them out. 😄