`#![feature]` may not be used on the stable release channel

[Arsaev]

Hi,

I'm on step 02_runtime_init and when i try to make qemu compilation fails with next error

Compiling kernel - rpi3
   Compiling tock-registers v0.6.0
error[E0554]: `#![feature]` may not be used on the stable release channel
 --> /Users/myuser/.cargo/registry/src/github.com-1ecc6299db9ec823/tock-registers-0.6.0/src/lib.rs:5:1
  |
5 | #![feature(const_fn)]
  | ^^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0554`.
error: could not compile `tock-registers`

To learn more, run the command again with --verbose.
make: *** [target/aarch64-unknown-none-softfloat/release/kernel] Error 101

Would be very thankful to any help with it.

[Arsaev]

Issue was in missing rust-toolchain file