1.4 release notes: Clarify change to `docker tag`

Minor clarification to the 1.4 release notes. I'm not sure what your policy is on changing the release notes after the release, or if changing this file will propagate to <https://docs.docker.com/release-notes/>, but anyway this wording would have saved me some head-scratching.

Also the 1.3.2 release notes state "The `--insecure-registry` flag of the `docker run` command" -- but the flag belongs to the main `docker` daemon command, not `docker run`. However the 1.3.2 release notes are gone from docs/sources/release-notes.md so I didn't attempt to fix this.

@fredlf you were the last person to touch this file, so you might want to look at this. Or just close it if I'm too late. Cheers. :-)