add short description of the project to readme

[danielblagy]

Section name is Introduction, it must be at the top of the page (after Table of Contents), include it in the Table of Contents

• give a concise description of what the project is about
• also include basic functionality (user cases) (from the notion page Introduction->About), don't include the pictures

reference on readme basic syntax https://docs.github.com/en/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax

[mrnkslv]

1. Created Introduction section at the top of the page:
   ## Introduction
   2)Included it in the Table of Contents :
   * [Introduction](#introduction)
   3)Wrote project description and described the functionality :

Budget-app is a personal finance app (cash organizer) with the following functionality: 
- Register in the application
- Log in to the application (if you have an account)
- View/add/edit/delete *Categories*
- View/add/edit/delete *Expenses*
- View/add/edit/delete *Incomes*
- View Reports