run.md states that the operator can override all defaults set in the Dockerfile, and explicitly says that `--expose` overrides the `EXPOSE` instruction. Neither of these are true. An `EXPOSE` instruction cannot be overridden, `--expose` can only add additional exposed ports.
This change fixes the instructions, and also takes the liberty of crisping up the grammar and phrasing in a place or two.
Signed-off-by: Spencer Brown <spencer@spencerbrown.org>