Fix typo in README

[yuyun2000]

Description
This pull request fixes a typographical error in the project's README file. Specifically, it removes a duplicate word "is" in a sentence regarding the possibility of self-managing a production Open edX instance. This change enhances the readability and professionalism of the documentation.

Affected User Roles: This change primarily impacts users reading the documentation, such as Developers and Operators.
Design Choices: No design changes were necessary, as this is a text correction.
Supporting information
No linked issues or discussions were pertinent to this change, as it is a straightforward documentation correction.

Testing instructions
Open the README file.
Verify that the sentence now reads "it is possible" instead of "it is is possible" in the referenced section.
Deadline
None.

Other information
This change is isolated to documentation and does not impact the codebase or require configuration changes. No dependencies or special concerns are associated with this correction.

[openedx-webhooks]

Thanks for the pull request, @yuyun2000!

What's next?

Please work through the following steps to get your changes 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

🔘 Submit a signed contributor agreement (CLA)

⚠️ We ask all contributors to the Open edX project to submit a signed contributor agreement or indicate their institutional affiliation.
Please see the CONTRIBUTING file for more information.

If you've signed an agreement in the past, you may need to re-sign.
See The New Home of the Open edX Codebase for details.

Once you've signed the CLA, please allow 1 business day for it to be processed.
After this time, you can re-run the CLA check by adding a comment below that you have signed it.
If the CLA check continues to fail, you can tag the @openedx/cla-problems team in a comment for further assistance.

🔘 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.

🔘 Let us know that your PR is ready for review:

Who will review my changes?

This repository is currently maintained by @openedx/wg-maintenance-edx-platform. Tag them in a comment and let them know that your changes are ready for review.

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.