code: function pipfileToRequirements() {
    if (
      !this.options.usePipenv ||
      !fse.existsSync(path.join(this.servicePath, 'Pipfile'))
    ) {
      return;
    }
  
    this.serverless.cli.log('Generating requirements.txt from Pipfile...');
  
    const res = spawnSync(
      'pipenv',
      ['lock', '--requirements', '--keep-outdated'],
      {
        cwd: this.servicePath
      }
    );
    if (res.error) {
      if (res.error.code === 'ENOENT') {
        throw new Error(
          `pipenv not found! Install it with 'pip install pipenv'.`
        );
      }
      throw new Error(res.error);
    }
    if (res.status !== 0) {
      throw new Error(res.stderr);
    }
    fse.ensureDirSync(path.join(this.servicePath, '.serverless'));
    fse.writeFileSync(
      path.join(this.servicePath, '.serverless/requirements.txt'),
      removeEditableFlagFromRequirementsString(res.stdout)
    );
  }
docs: pipenv install