Added Introduction to DataFrames course by Bogumił Kamiński (#8778)

* Update free-courses-en.md

* Update courses/free-courses-en.md

Co-authored-by: Sharan J <50091666+shrn01@users.noreply.github.com>

* Apply suggestions from code review

Co-authored-by: Sharan J <50091666+shrn01@users.noreply.github.com>

courses/free-courses-en.md

@@ -922,6 +922,7 @@
 
 * [Decision Making Under Uncertainty using POMDPs.jl](https://www.youtube.com/playlist?list=PLP8iPy9hna6QPqk4N8eBk0oXzLrLbOtTA) - The Julia Programming Language
 * [GeoStats.jl Tutorials](https://www.youtube.com/playlist?list=PLsH4hc788Z1f1e61DN3EV9AhDlpbhhanw) - Julio Hoffimann (YouTube)
+* [Introduction to DataFrames.jl](https://juliaacademy.com/p/introduction-to-dataframes-jl) - Bogumił Kamiński (JuliaAcademy)
 * [Julia Tutorials (Basic)](https://www.youtube.com/playlist?list=PLP8iPy9hna6SCcFv3FvY_qjAmtTsNYHQE) - The Julia Programming Language (YouTube)