code: function addVendorHelper() {
    if (this.options.zip) {
      if (this.serverless.service.package.individually) {
        return BbPromise.resolve(this.targetFuncs)
          .map(f => {
            if (!get(f, 'package.include')) {
              set(f, ['package', 'include'], []);
            }
            if (!get(f, 'module')) {
              set(f, ['module'], '.');
            }
            f.package.include.push('unzip_requirements.py');
            return f;
          })
          .then(functions => uniqBy(functions, func => func.module))
          .map(f => {
            this.serverless.cli.log(
              `Adding Python requirements helper to ${f.module}...`
            );
  
            return fse.copyAsync(
              path.resolve(__dirname, '../unzip_requirements.py'),
              path.join(this.servicePath, f.module, 'unzip_requirements.py')
            );
          });
      } else {
        this.serverless.cli.log('Adding Python requirements helper...');
  
        if (!get(this.serverless.service, 'package.include')) {
          set(this.serverless.service, ['package', 'include'], []);
        }
  
        this.serverless.service.package.include.push('unzip_requirements.py');
  
        return fse.copyAsync(
          path.resolve(__dirname, '../unzip_requirements.py'),
          path.join(this.servicePath, 'unzip_requirements.py')
        );
      }
    }
  }
docs: Add the vendor helper to the current service tree.
  @return {Promise}