Update README.md [ci skip]

Author: olekscode

README.md

@@ -7,7 +7,15 @@
 [![Pharo version](https://img.shields.io/badge/Pharo-7.0-%23aac9ff.svg)](https://pharo.org/download)
 [![Pharo version](https://img.shields.io/badge/Pharo-8.0-%23aac9ff.svg)](https://pharo.org/download)
 
-DataFrame is a tabular data structure for data analysis in [Pharo](https://pharo.org/), similar to [pandas](https://pandas.pydata.org/) in Python or [data.frame](https://www.rdocumentation.org/packages/base/versions/3.5.2/topics/data.frame) in R. It is a spreadsheet-like collection with an API specifically designed for data exploration and analysis.
+DataFrame is a tabular data structure for data analysis in [Pharo](https://pharo.org/).
+
+For more information, please read [Data Analysis Made Simple with Pharo DataFrame](https://github.com/SquareBracketAssociates/Booklet-DataFrame) - a booklet that serves as the main source of documentation for the DataFrame project. It describes the complete API of DataFrame and DataSeries data structures, and provides examples for each method.
+
+## What are data frames?
+
+Data frames are the one of the essential parts of the data science toolkit. They are the specialized data structures for tabular data sets that provide us with a simple and powerful API for summarizing, cleaning, and manipulating a wealth of data sources that are currently cumbersome to use.
+
+A data frame is like a database inside a variable. It is an object which can be created, modified, copied, serialized, debugged, inspected, and garbage collected. It allows you to communicate with your data quickly and effortlessly, using just a few lines of code. DataFrame project is similar to [pandas](https://pandas.pydata.org/) library in Python or built-in [data.frame](https://www.rdocumentation.org/packages/base/versions/3.5.3/topics/data.frame) class in R.
 
 [![Screenshot](img/example.png)](https://raw.githubusercontent.com/PolyMathOrg/DataFrame/master/img/example.png)