suggest a compatible shell for running setup-toolchain.sh
suggest a compatible shell for running setup-toolchain.sh

setup-toolchain.sh uses "[[" which is a bash builtin, but the guide
suggests running it with sh.  On Ubuntu, /bin/sh points to dash and
running the script as described fails.

graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust