code: function addTag(tag, options) {
      addToCommon({
          schemaKey: schemaIds.tag,
          object: tag,
          targetObject: state.common.tags,
          displayName: 'Tag'
      }, options);
  }
docs: Adds a common tag for later use.
  @paramSchema tag ./lib/schemas/tag.json
  @param {object} tag Allows adding meta data to a single tag that is used by the Operation Object. It is not mandatory to have a Tag Object per tag used there.
  @param {string} tag.name - Required. The name of the tag.
  @param {string} [tag.description] - A short description for the tag. GFM syntax can be used for rich text representation.
  @param {object} [tag.externalDocs] - information about external documentation
  @param {string} [tag.externalDocs.description] - A short description of the target documentation. GFM syntax can be used for rich text representation.
  @param {string} tag.externalDocs.url - Required. The URL for the target documentation. Value MUST be in the format of a URL.
  @param {AddCommonItemOptions} [options] - Options to apply when adding the provided item.
  @returns {void}
  @example
  var swagger = require('swagger-spec-express');
  swagger.common.addTag({
  name: "Info",
  description: "Info about the api"
  });
  //...
  router.get('/', function (req, res) {
  //...
  }).describe({
  //...
  tags: ["Info"],
  //...
  });