Add code block to code in documentation of `List::rebase_onto`
Add code block to code in documentation of `List::rebase_onto`

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