add index file

index.md

+---
+title: #  R for beginners
+---
+
+# R for beginners
+
+1.[Introduction to R and RStudio](./session_1.html)
+2.[introduction to Tidyverse](./session_2.html)
+3.[Transformations with ggplot2](./session_3.html)
+4.[data transformation](./session_4.html)
+5.[Pipping and grouping](./session_5.html)
+6.[tidydata](./session_6.html)
+7.[String & RegExp](./session_7.html)
+8.[Factors](./session_8.html)
+