Add obj-c to swift in the analogy

[PineappleRind]

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[jonmeow]

Can you please sign the CLA? We can't accept contributions from anyone who hasn't signed it.

That said, assigning to @chandlerc because the README was carefully reviewed already.

[jonmeow]

I think it's important to note that the README's content will not be as exhaustive as what's covered in presentations, and part of that includes talking about what's different about each successor language approach. Rather than adding Swift along with an explanation about how it's different from the other approaches, I think it's better to keep omitting it.

Since this PR has been sitting for a month without more support, I'm going to close it now.