code: func (c *Config) Set(sectionName, key, value string) {
  	for i, sect := range c.sections {
  		if sect.name == sectionName {
  			for j, opt := range sect.options {
  				if opt.name == key {
  					c.sections[i].options[j].value = value
  					return
  				}
  			}
  			c.sections[i].options = append(sect.options, option{key, value})
  			return
  		}
  	}
  
  	c.sections = append(c.sections, section{
  		name:    sectionName,
  		options: []option{{key, value}},
  	})
  }
docs: // Set sets a value for an option in a section. If the option exists, it's
  // value will be overwritten. If the option does not exist, it will be added.
  // If the section does not exist, it will be added and the option added to it.