refactor: improve double dirname and add more documentation of Open edX

[MaferMazu]

Description

This PR:

• Improve double dirname

Pass the $levels parameter to the dirname() call instead of using nested dirname() calls (PHP >= 7.0)
| | (Modernize.FunctionCalls.Dirname.Nested)

• Add more documentation

Additional information

This changes come from common mistakes in WordPress plugins. Mistakes related:

Incorrect "Tested up to" parameter (readme file):
This should be the major version of WordPress that this plugin has been tested on. In the case of new plugins, we require it to be the latest version. This is necessary for plugins to be visible in the repository.
Example: Tested up to: 6.3

...

Failure to disclose third party or external services (readme file):
Any usage of third party services, such as connecting to an external API, needs to be documented in the readme file.

How to document this:
Clearly explain that your plugin is relying on a third party service and under what circumstances.
Provide a link to the service.
Provide a link to the service's terms of use and/or privacy policies.
There is no specific format for this, but please make sure you provide enough info and links to terms of use / privacy policies.

Checklist for Merge

• Tested in a remote environment
• Updated documentation
• Rebased master/main

[openedx-webhooks]

Thanks for the pull request, @MaferMazu! Please note that it may take us up to several weeks or months to complete a review and merge your PR.

Feel free to add as much of the following information to the ticket as you can:

• supporting documentation
• Open edX discussion forum threads
• timeline information ("this must be merged by XX date", and why that is)
• partner information ("this is a course on edx.org")
• any other information that can help Product understand the context for the PR

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Please let us know once your PR is ready for our review and all tests are green.

[felipemontoya]

Looks good to me. Thanks @MaferMazu

[openedx-webhooks]

@MaferMazu 🎉 Your pull request was merged! Please take a moment to answer a two question survey so we can improve your experience in the future.