Reformat the home page organization section

The mentor for this issue is @geoffreynyaga

## Background

1. The [**How this documentation is organized**](https://canonical-robotics.readthedocs-hosted.com/en/latest/#how-this-documentation-is-organized) section on the Robotics Documentation home page is displayed as a card-style table. This interrupts the page layout. Reformat the section as a list, following these documentation home-page examples:
- [Multipass: How this documentation is organized](https://canonical.com/multipass/docs/latest/#how-this-documentation-is-organized)
- [Anbox Cloud: How this documentation is organised](https://canonical.com/anbox-cloud/docs/#how-this-documentation-is-organised)

2. The heading (i.e How this documentation is organized) should also be a level-2 heading.

## Prerequisites

Basic familiarity with reStructuredText (reST) and Git is required.

## What you will learn

* How to edit reST source files.
* How Canonical documentation home pages are structured.
* How to contribute a documentation change through Git and GitHub.

## Task

1. In the [`canonical/robotics_documentation`](https://github.com/canonical/robotics_documentation) repository, update `docs/index.rst`.
2. Replace the card-style `list-table` under **How this documentation is organized** with a list view.
3. Change **How this documentation is organized** to a level-2 heading.
4. Use the linked Multipass and Anbox Cloud pages as formatting references.
5. Open a pull request against the repository and sign the [Canonical contributor license agreement](https://ubuntu.com/legal/contributors).

## Outcome

The Robotics Documentation home page displays its documentation types in a readable list, and the section heading is level 2.

## Resources

* [Robotics Documentation source file](https://github.com/canonical/robotics_documentation/blob/main/docs/index.rst)
* [Multipass documentation example](https://canonical.com/multipass/docs/latest/#how-this-documentation-is-organized)
* [Anbox Cloud documentation example](https://canonical.com/anbox-cloud/docs/#how-this-documentation-is-organised)

Start with docs/index.rst and inspect the existing list-table under “How this documentation is organized.” Compare the linked Multipass and Anbox Cloud pages, then replace the card-style table with a list and make the section heading level 2. Done means the rendered home page shows a readable list and the heading has the requested level; open a pull request and complete the contributor license agreement.

Written by the indexing model from the issue text.