docs: restore the pointer to the plug-in and frontend Quickstarts

[rawsun007]

first_openedx_pr.rst carries this paragraph as an RST comment, so it has never rendered:

.. This Quickstart is written for first-time contributors to the Open edX project.
   If you are a plug-in developer or a frontend developer, please see our
   :doc:`Quickstart guide for plug-in developers <setup_a_plugin_dev_environment>`
   or our :doc:`Quickstart for frontend developers <setup_an_mfe_dev_environment>`.

It was live text when the page was added in 0a6371f. f2f264e — "docs: Remove empty placeholder files" — deleted the two Coming Soon! placeholders it linked to and commented the paragraph out in the same commit, with the note:

All of these now have tickets on the docs project board so we don't need the empty place-holders. We can add the files back when there is [content].

That content exists now. tutor_quickstart_dev.rst is "Tutor Quickstart (Developer)" and tutor_quickstart_mfe.rst is "Tutor Quickstart (MFE Development)", which are the two audiences the paragraph was sending away. This points at them by the :ref: labels those pages already define, so the signpost renders again rather than sitting in a comment.

Nothing else on the page changes, and no new label is introduced.

Because the targets were inside a comment, Sphinx never resolved them, so there was no build warning to catch this — it only shows up by reading.

The wording of the replacement is my reading of the original intent: "plug-in developer" became "setting up a development environment", since tutor_quickstart_dev is the general dev-environment guide rather than a plug-in-specific one. If you would rather it said something else, or would rather the paragraph stay commented, say so and I will adjust or close.

Verification: sphinx -b html source builds with zero warnings, and the rendered page contains both links:

tutor_quickstart_dev.html#tutor-qs-dev      | Tutor Quickstart (Developer)
tutor_quickstart_mfe.html#tutor-for-mfe-qs  | Tutor Quickstart (MFE Development)

AI disclosure, per the Open edX AI Contribution Policy: written by Claude Opus 5 (Claude Code) running under my account, which is one of the permitted tools. It found the commented block, traced the two commits above, chose the replacement targets and ran the docs build. I have not read the diff line by line myself yet.

[openedx-webhooks]

Thanks for the pull request, @rawsun007!

This repository is currently maintained by @openedx/wg-maintenance-docs.openedx.org.

Once you've gone through the following steps feel free to tag them in a comment and let them know that your changes are ready for engineering review.

🔘 Get product approval

If you haven't already, check this list to see if your contribution needs to go through the product review process.

• If it does, you'll need to submit a product proposal for your contribution, and have it reviewed by the Product Working Group.
  • This process (including the steps you'll need to take) is documented here.
• If it doesn't, simply proceed with the next step.

🔘 Provide context

To help your reviewers and other members of the community understand the purpose and larger context of your changes, feel free to add as much of the following information to the PR description as you can:

• Dependencies

  This PR must be merged before / after / at the same time as ...

• Blockers

  This PR is waiting for OEP-1234 to be accepted.

• Timeline information

  This PR must be merged by XX date because ...

• Partner information

  This is for a course on edx.org.

• Supporting documentation
• Relevant Open edX discussion forum threads

🔘 Get a green build

If one or more checks are failing, continue working on your changes until this is no longer the case and your build turns green.

Details

---

Where can I find more information?

If you'd like to get more details on all aspects of the review process for open source pull requests (OSPRs), check out the following resources:

• Overview of Review Process for Community Contributions
• Pull Request Status Guide
• Making changes to your pull request

When can I expect my changes to be merged?

Our goal is to get community contributions seen and reviewed as efficiently as possible.

However, the amount of time that it takes to review and merge a PR can vary significantly based on factors such as:

• The size and impact of the changes that it introduces
• The need for product review
• Maintenance status of the parent repository

💡 As a result it may take up to several weeks or months to complete a review and merge your PR.