Add new target

[stappersg]

Because switching to a new default did scare me.

[stappersg]

FWIW: It is switching to a new default does scare me.

I mean that I haven't tried / verified the purposed patch.

Thing that I'm expressing is that I read the rustup default esp as say goodbye to your working rust environment.
Probably more people are worried about hosing their system, about losing a working rust environment.

[MabezDev]

Your changes won't work, esp is a toolchain, not a target. I've updated the README to point to the installation docs of the book. Please feel free to open a PR against the book instead :).

[stappersg]

I've updated the README to point to the installation docs of the book.

That will be commit 1f20253 thanks for that update.