func ReadMirrorsFile(opath string) (*Mirrors, error) {
	yml, err := ioutil.ReadFile(opath)
	if err != nil {
		return nil, err
	}
	ov, err := FromYaml(yml)
	if err != nil {
		return nil, err
	}
	return ov, nil
}
ReadMirrorsFile loads the contents of an mirrors.yaml file.
package mirrors
import (
	"io/ioutil"
	"sort"
	"strings"
	"gopkg.in/yaml.v2"
)
type Mirrors struct {
	Repos MirrorRepos `yaml:"repos"`
}
func (ov *Mirrors) Marshal() ([]byte, error) {
	yml, err := yaml.Marshal(&ov)
	if err != nil {
		return []byte{}, err
	}
	return yml, nil
}
func (ov *Mirrors) WriteFile(opath string) error {
	o, err := ov.Marshal()
	if err != nil {
		return err
	}
	return ioutil.WriteFile(opath, o, 0666)
}