Update reference link for joins in R

Author: bioinfo-arctic

Spring_2026/Exercise_Linux_R_data_wrangling.md

@@ -78,6 +78,6 @@ In the **tidyverse** package, what is the difference between the following funct
 - `right_join()`
 - `full_join()`
 
-Reference: [Joins in R for Data Science](https://r4ds.hadley.nz/joins.html#sec-mutating-joins)
+Reference: [Joins in R for Data Science](https://r4ds.hadley.nz/joins.html#how-do-joins-work)
 
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