Remove IRC mention from README.md

[rohitgeddam]

Removed IRC mention (#machomebrew). This IRC channel is not being actively used by our community ( 0 active users ).

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew tests with your changes locally?
• Have you successfully run brew man locally and committed any changes?

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[Rylan12]

Thanks, @rohitgeddam!

The CI failures are unrelated. Once they've been resolved this will be 👍.