docs: add Assignedtask with its description and constraints

[yuki-92c]

Overview

• I added the descriptions and constraints of AssignedTask

Changes

AssignedTask - 割当タスク

taskId

• TaskId is the UUID

title

• The owner can set a title as they prefer. This title can be modified at any time.

Constraints:

• It must be between 1 and 20 characters in length.

description

• The owner can provide details for the task. This description can be modified at any time.

Constraints:

• The description must be between 10 and 120 characters.

completed

• Whether the task is completed or not.

Assignee Checklist:

• [x] The base branch is correct (no accidental merges)

Reviewer Checklist

• Code readability and simplicity
• Follows best practices and coding standards
• Understandable and maintainable code

[yuki-92c]

Thank you for making changes, but could you revise the PR title too as it does not follow our standard?

thanks for the comment and edited the title.