Auto merge of #6150 - flip1995:backport_doc_update, r=ebroto
Auto merge of #6150 - flip1995:backport_doc_update, r=ebroto

Update backport documentation to the subtree workflow

changelog: none

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