Auto merge of #1642 - jonahwilliams:patch-1, r=RalfJung
Auto merge of #1642 - jonahwilliams:patch-1, r=RalfJung

Fix README.md typo "extend" -> "extent"

Just something I noticed while reading.

rust-lang/miri,rust-lang/miri,rust-lang/miri,rust-lang/miri