Add #rust-embedded to community page

[thumphries]

I was happy to find the #rust-embedded channel, and noticed it wasn't in this list. I found it after spamming #rust-osdev.

I'm not sure how to go about spreading this change to the internationalised versions of the site. If someone could advise me how to proceed I'll gladly update this PR.

[rust-highfive]

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

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[nikomatsakis]

Looks good to me. I'm not sure about i18n either, though. =)

[nikomatsakis]

@steveklabnik or @brson, do we have a policy there?

[steveklabnik]

@steveklabnik or @brson, do we have a policy there?

The policy is basically that they're done on a best-effort basis. So leaving them alone is fine.