Implement main page of app description: https://github.com/rolling-scopes-school/tasks/blob/master/tasks/stage-2/rs-lang/rslang.md#%D0%B3%D0%BB%D0%B0%D0%B2%D0%BD%D0%B0%D1%8F-%D1%81%D1%82%D1%80%D0%B0%D0%BD%D0%B8%D1%86%D0%B0-%D0%BF%D1%80%D0%B8%D0%BB%D0%BE%D0%B6%D0%B5%D0%BD%D0%B8%D1%8F-40 base route: /main
