add README for reconfigurator-exec-unsafe - #11243

control: job assigned to worker 01M1Q9H932CPBJZ2HNQQE061WQ [factory aws, i-097ae1e891c7b52e1] (queued for 49 s)
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task: starting task 0: "setup"
task: process exited: duration 4132 ms, exit code 0
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task: starting task 1: "rust-toolchain"
task: process exited: duration 15108 ms, exit code 0
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task: starting task 2: "authentication"
task: process exited: duration 15 ms, exit code 0
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task: starting task 3: "clone repository"
task: process exited: duration 13747 ms, exit code 0
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task: starting task 4: "build"
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| info: running `cargo check --bins` on zone-setup (376/376)
| warning: profile package spec `blake2b_simd` in profile `dev` did not match any packages
| warning: profile package spec `rust-argon2` in profile `dev` did not match any packages
|     Checking uzers v0.12.2
|     Checking zone-setup v0.1.0 (/work/oxidecomputer/omicron/zone-setup)
|     Finished `dev` profile [unoptimized + debuginfo] target(s) in 1.72s
| 
| real    14:16.669188390
| user    21:26.998051604
| sys      4:22.193160155
| trap        0.336387064
| tflt        0.578266697
| dflt        0.885141516
| kflt        0.004852392
| lock  1:29:29.539994635
| slp   1:42:13.757993379
| lat        56.979722307
| stop     4:05.253774154
task: process exited: duration 987897 ms, exit code 0
|W| found 0 output files