Adopt rust-by-example as a subteam of lang-docs

[traviscross]

We're working to move things out from under the launching-pad team to more appropriate places. It makes the most sense for the rust-by-example working group to be adopted as a subteam of lang-docs, so let's do that.

Note that, in doing this, we'll make it a proper subteam rather than a working group.

See:

• [launching-pad] Find a home for the "Rust By Example" Working Group leadership-council#139

cc @ehuss @marioidival @jamesmunns

[traviscross]

@jamesmunns and I had a good talk. He suggested that it would be valuable to add some further context to this PR.

The first bit of context is that I'm making this PR with my lang-docs, lang, and lang-ops hats on -- that is, the hat of a member of the adopting team, its parent team, and the team that supports that parent team and tends to handle many administrative and policy matters like this -- not with my council hat on.

Regarding the lang-docs hat, while, in practice, @ehuss and I tend to handle much of the coordination work for lang-docs, this should of course be approved by one or both of the current leads for lang-docs, @ehuss and/or @JohnTitor. This PR can be seen as my suggestion to my fellow team members about the appropriate handling. As it is, @ehuss and I had discussed this ahead of time.

I was prompted to make this PR by @chriskrycho following up to my proposal in rust-lang/leadership-council#123 after talking with @carols10cents regarding the handling of the book team. With that resolved, and that PR up in #1636, it seems clear that rust-by-example should be handled in the same way, as @jamesmunns had proposed in rust-lang/leadership-council#139 (comment) and that @nikomatsakis, the lead of the adopting team's parent team, had responded favorably to in rust-lang/leadership-council#139 (comment), and that the next step is for the adopting team to adopt the team to be adopted, so that's what this PR proposes to do.

On the council side, @jamesmunns is of course the one coordinating this, and is of course in my view doing a great job in that. Thanks to James for opening the tracking issues such as the one here, for bringing the various parties together, and for updating the council on all the various progress on this endeavor.

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Putting on my council hat for a moment, I suppose we might consider the question of whether each of (or each specific batch of) these moves requires an FCP from the council. My own feeling is that it's probably not necessary to require such process for moves of a group out from under launching-pad, where both the group and the adopting team agree on the handling (and where no other potentially-adopting team is making a claim), especially given our preexisting consensus that moving such groups out from launching-pad to more appropriate teams is what we'd like to see happen. But I'm curious to hear what @jamesmunns thinks, and if it's at all unclear we should of course raise this topic in our next council meeting on 2025-01-17.