Feature Request - Add a landing page with community guidelines (Similar to README.md) in github

**Is your feature request related to a problem? Please describe.**
I want to submit a feature request. I want to add some Q&A forum rules / best practices for the community to follow in the home page.

**Describe the solution you'd like**
I want to be able to add a landing page detailing community rules and guidelines for posters.

**Describe alternatives you've considered**
/**admin/css-html** - I was able to add some rudimentary js-based solution to add some content on the home page (if (document.location == 'ABC') then display some content

Start by reviewing the existing /admin/css-html approach mentioned in the issue and then locate the current home-page entry point. Done means the home page provides a landing page containing community rules and posting guidelines, without relying on the described rudimentary workaround.

索引モデルが issue の本文から書いたものです。