Fix Typos and Improve Documentation Across Multiple Files

[Dimitrolito]

This PR addresses various typographical issues across multiple documentation files, including:

• Corrected hyphenation in compound adjectives such as "built-in" and "right-clicking".
• Fixed grammatical errors such as missing words and articles (e.g., "will be able" instead of "will able").
• Adjusted formatting for clarity and consistency, including the use of "cross-references" with a hyphen.

Files affected:

• migrating-keys.md
• switch-clients.md
• contribution-guidelines.md
• install-with-docker.md
• prysmctl.md
• slasher.md

These updates aim to improve the readability and correctness of the documentation.