Change user manual structure

[javimed]

Description

Checks

Docs building

• [ ] Compiles without warnings.

Code formatting and web optimization

• [ ] Uses three spaces indentation.
• [ ] Adds or updates meta descriptions accordingly.
• [ ] Updates the redirects.js script if necessary (check this guide).

Writing style

• [ ] Uses present tense, active voice, and semi-formal registry.
• [ ] Uses short, simple sentences.
• [ ] Uses bold for user interface elements, italics for key terms or emphasis, and code font for Bash commands, file names, REST paths, and code.