Add the Large Instances working group to the description

[antoviaque]

Based on the discussion and steps from https://github.com/openedx/tutor-contrib-multi/issues/12

See also https://openedx.atlassian.net/wiki/spaces/COMM/pages/3655008783/Large+Instances+-+DevOps+Sub-Working+Group

[openedx-webhooks]

Thanks for the pull request, @antoviaque! 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.

[openedx-webhooks]

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