1. start page

[IlyaKhokhanov]

• Make start page.
• Take data from json of selected schoolbook and show this data in checkboxes.
• Saving selected schoolbook and data from checkbox with useState and give this data to other pages with useContext.
• Used react-router-dom for navigation.
• Used immer for immutable state.

[jahglow]

так, на гитхаб страницы должно деплоиться само работающее приложение а не readme)