Some minor fixes for cli docs

This Pull Request includes following 2 commits

**Fix duplication of --mtu option's description of daemon doc**

--mtu option's description wass duplicated by commit baa70e9 like
```
  --mtu=0: Set the containers network MTU; if no value is provided: default to the default route MTU or 1500 if not default route is available
  -p, --pidfile="/var/run/docker.pid": Path to use for daemon PID file
  -r, --restart=true: Restart previously running containers
  -s, --storage-driver="": Force the docker runtime to use a specific storage driver
  -e, --exec-driver="native": Force the docker runtime to use a specific exec driver
  -v, --version=false: Print version information and quit
  --mtu=0: Set the containers network MTU; if no value is provided: default to the default route MTU or 1500 if no default route is available
```

**Add -t and -v option to images subcommand doc**

Images subcommand has -t option as synonym of --tree and -v option as synonym of --viz.
The doc described --tree and --viz but there were no -t and -v.