docs: improve the doc structure

[profanis]

PR Checklist

Please check if your PR fulfills the following requirements:

• [ ] The commit message follows our guidelines: https://github.com/ngxs/store/blob/master/CONTRIBUTING.md#commit
• [ ] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[ ] No

Other information

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[bundlemon[bot]]

BundleMon (Integration Projects)

Unchanged files (2)

Status | Path | Size | Limits :------------: | ------------ | :------------: | :------------: :white_check_mark: | Main bundles(Gzip)
_{hello-world-ng17/dist-integration/main.(hash)
.js}
| 68.43KB | +1% :white_check_mark: | Main bundles(Gzip)
_{hello-world-ng16/dist-integration/main.(hash)
.js}
| 66.94KB | +1%

No change in files bundle size

Final result: :white_check_mark:

View report in BundleMon website ➡️

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Current branch size history | Target branch size history

[codeclimate[bot]]

Code Climate has analyzed commit 7c91e58b and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (50% is the threshold).

This pull request will bring the total coverage in the repository to 95.3% (0.0% change).

View more on Code Climate.

[arturovt]

P.S. I merged this so that Fanis can proceed with Mark's comments in subsequent PRs.