docs(main_page): enrich front page

[TakaHoribe]

Description

update front page

Pre-review checklist for the PR author

The PR author must check the checkboxes below when creating the PR.

• I've confirmed the contribution guidelines.
• The PR follows the pull request guidelines.

In-review checklist for the PR reviewers

The Reviewers must check the checkboxes below before approval.

• The PR follows the pull request guidelines.

Post-review checklist for the PR author

The PR author must check the checkboxes below before merging.

• There are no open discussions or they are tracked via tickets.

After all checkboxes are checked, anyone who has write access can merge the PR.

[github-actions]

Documentation URL: https://autowarefoundation.github.io/autoware-documentation/pr-526/
Modified URLs:

• https://autowarefoundation.github.io/autoware-documentation/pr-526/
• https://autowarefoundation.github.io/autoware-documentation/pr-526/

[mitsudome-r]

Other parts LGTM.

[dkoldaev]

This is way more friendlier for a beginner (from a beginner prospective)! Good job!

[dkoldaev]

Looks very nice now! I hope we can improve more pages to this standard!