Adding Medium Articles

Create README.md

Updates for SARIMA, ARMA+GARCH, and GARCH notebooks

Updating data, EDA and Preprocessing files

Adding code to analyse S&P 500 Prices and Returns using Facebook Prophet

Adding code to analyse S&P 500 Volatility

Adding code to analyse and forecast S&P 500 Prices

Adding code to analyse and forecast S&P 500 Returns

Adding dataset and code for Preprocessing and EDA