docs: update README (take over #131)

[Okabe-Junya]

take over #131

Proposed Changes

I have structured the README. Only the essential information is retained in the README, and I've made changes to store each document in the docs directory. This is based on the structure of the CodeQL repository.

(If there are any rules or standards we must adhere to within the GitHub organization, I would like to make further adjustments to comply with them.)

Readiness Checklist

In addition, I made the following changes:

• Removal of the Table of Contents: GitHub's markdown preview has an automatic table of contents generation feature. It's unlikely we need to maintain this ourselves.
• Removal of permalinks to each document: Most users should notice that the documents are stored in the docs directory. Managing permalinks can be cumbersome, so I believe it's best to remove them.

Author/Contributor

Note: In this PR, since only documentation updates are being made, I don't anticipate any linting or testing issues to arise.

• If documentation is needed for this change, has that been included in this pull request
• run make lint and fix any issues that you have introduced
• run make test and ensure you have test coverage for the lines you are introducing

Reviewer

• Label as either bug, documentation, enhancement, infrastructure, or breaking

[Okabe-Junya]

It seems there are still some points that need correction. After making the changes, I will undraft the PR.

[zkoppert]

it looks like a few of the docs like the json output, measuring time and others in the docs directory aren't all referenced in the README. I think each doc should at least get a mention in the readme.

[Okabe-Junya]

Thank you for the wonderful review!!

Regarding "I think each doc should at least get a mention in the readme.", are you suggesting adding a section with links to each item as in the following example?

## links

- [Assigning teams instead of individuals](./docs/assign-team-instead-of-individual.md)
- ...

[zkoppert]

Yes that would be great.

[Okabe-Junya]

Thank you for the wonderful review!! I made three changes.

1. reverted the changes to the footnote.
2. reverted the changes to the example use case.
3. added a section with links to each document in the README.

[zkoppert]

Awesome! Thank you so much @Okabe-Junya for leading this to completion!! Really appreciate all your contributions to this project! 🎉 🚀

[spier]

@zkoppert looks like merging this has accidentally done some of the changes that we did in #137 prior to this.

[zkoppert]

@spier Good Catch! I'll get that corrected. #140