docs: 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!

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[kdmccormick]

Thanks!

[kdmccormick]

@yuyun2000 Before we can merge your PR, we need you to sign the Open edX CLA: https://openedx.org/cla

You can ignore the rest of the CI failures--once your CLA is all set, I'll re-run those, ensure they pass, and then merge this PR.

[kdmccormick]

Please also use a conventional commit message. For example, docs: Fix typo in README would be appropriate.

[yuyun2000]

Please also use a conventional commit message. For example, docs: Fix typo in README would be appropriate.

Sorry, this is my first time contributing to a large project, thank you for your guidance！

[kdmccormick]

No problem, glad to help!