The actual release process had quite diverged from what was written here, also clarify things a bit and update the style to be like our other .md files. More like "rewrite the entire thing".
Best to read the rendered version: https://github.com/laanwj/bitcoin/blob/2016_04_update_release_process/doc/release-process.md
Closes #7595 as well by removing the hardcoded version number from verify.sh.