modify index page and change extension

index.md

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-title: #  R for beginners
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-
-# R for beginners (2022)
-
-  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)
-

index.qmd

+# R for beginners (2022) {.unnumbered}
+
+  1. [Introduction to R and RStudio](session1/session_1.html)
+  2. [Introduction to Tidyverse](session2/session_2.html)
+  3. [Transformations with ggplot2](session3/session_3.html)
+  4. [Data transformation](session4/session_4.html)
+  5. [Pipping and grouping](session5/session_5.html)
+  6. [Tidydata](session6/session_6.html)
+  7. [String & RegExp](session7/session_7.html)
+  8. [Factors](session8/session_8.html)
+