Improve fetch document

[asmanp2012]

Description

document of options and parameters of fetch function

PR Checklist

Please check if your PR fulfills the following requirements:

• Open an issue for bug report or feature request and mention it to this PR.
• The commit message follows our guidelines: https://github.com/AliMD/vatr/blob/main/CONTRIBUTING.md#commit-message-format
• All methods have proper description in jsdocs format with @example section.
• Docs have been added / updated (for bug fixes / features).
• I have performed a self-review of my own code.

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other... Please describe:

Does this PR introduce a breaking change?

• Yes
• No

Other information

[github-actions]

Pull Request closed and locked due to lack of activity.
If you'd like to build on this closed PR, you can clone it using this method: https://stackoverflow.com/a/14969986
Then open a new PR, referencing this closed PR in your message.