grammar fix

[chrstfer]

Summary

• I noticed a small mistake with the contribution guidelines, and what better for a first contribution?
  • "When you ready..." -> "When you're ready..."

Issue

Is this necessary for such a small change?

Lasting Changes (Technical)

• None

Checklist

• [x] Documentation (if necessary)
• [N/A] Tests (integration test/unit test)
• [N/A] Integration Tests Passed
• [N/A] Code Review

[chrstfer]

I may add more as I further read the docs. I'll edit here when I'm done doing so to signal that my branch fix/contributing-docs is ready to merge.