R resources from mlr-wp

What can we link to from

https://institute-and-faculty-of-actuaries.github.io/mlr-blog/

Items we could consider:
* https://institute-and-faculty-of-actuaries.github.io/mlr-blog/post/intro-to-r/
* https://institute-and-faculty-of-actuaries.github.io/mlr-blog/post/tidyverse/
* https://institute-and-faculty-of-actuaries.github.io/mlr-blog/post/datatable/
* https://institute-and-faculty-of-actuaries.github.io/mlr-blog/post/f-intro_glm_gam_xgboost/

But only if it fits well with other content - no need to duplicate otherwise.

Review the cookbook's existing content and compare it with the four mlr-blog URLs listed in the issue. Determine whether each resource fits an existing section without duplicating material; the issue does not name a destination file, so the appropriate location must be identified before adding links.

索引モデルが issue の本文から書いたものです。