Link to FFI in Concurrency chapter

[corincerami]

No description provided.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @brson (or someone else) soon.

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[steveklabnik]

@bors: r+ rollup

[bors]

📌 Commit 42e3f1d has been approved by steveklabnik

[steveklabnik]

Thanks so much!

[corincerami]

@steveklabnik happy to help. I've been reading through the book lately, so when I see something I wish was clearer, I figure why not fix it?

[steveklabnik]

Absolutely. :) In general, more links like this are always good, so feel free to send more!

[bors]

⌛ Testing commit 42e3f1d with merge 81b3b27...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt