Update README.md with JuliaAcademy reference (#2294)

README.md

@@ -15,6 +15,13 @@ Tools for working with tabular data in Julia.
 **Maintenance**: DataFrames is maintained collectively by the [JuliaData collaborators](https://github.com/orgs/JuliaData/people).
 Responsiveness to pull requests and issues can vary, depending on the availability of key collaborators.
 
+**Learning**: New to DataFrames.jl? Check out our
+[free Julia Academy course](https://juliaacademy.com/p/introduction-to-dataframes-jl)
+which will walk you through how to use DataFrames.jl.
+You can also check out
+[Bogumił Kamiński's DataFrames.jl tutorial](https://github.com/bkamins/Julia-DataFrames-Tutorial)
+that is available on GitHub.
+
 [docs-latest-img]: https://img.shields.io/badge/docs-latest-blue.svg
 [docs-latest-url]: http://JuliaData.github.io/DataFrames.jl/latest/