Rollup merge of #5516 - flip1995:doc_release, r=phansch
Rollup merge of #5516 - flip1995:doc_release, r=phansch

Add a note to the beta sections of release.md

changelog: none

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