Add rust-by-example repo under automation

[Kobzol]

Repo: https://github.com/rust-lang/rust-by-example

It seems that highfive is no longer used by the repo, so I didn't keep it.

CC @marioidival

Extracted from GH:

org = "rust-lang"
name = "rust-by-example"
description = "Learn Rust with examples (Live code editor included)"
bots = []

[access.teams]
core = "admin"
highfive = "write"
security = "pull"
wg-rust-by-example = "write"

[access.individuals]
pietroalbini = "admin"
rylev = "admin"
rustbot = "write"
Mark-Simulacrum = "admin"
rust-lang-owner = "admin"
marioidival = "write"
jdno = "admin"
rust-highfive = "write"
badboy = "admin"