Correct grammar in R tute

Author: hyanwong

tskitr.md

@@ -44,7 +44,7 @@ n
 The `$` operator can also be used to call methods, for example, the 
 {meth}`~TreeSequence.simplify` method associated with the tree sequence.
 The method parameters are given as native R objects
-(but note that object IDs are still use tskit's 0-based indexing system).
+(but note that object IDs still use tskit's 0-based indexing system).
 
 ```{code-cell}
 reduced_ts <- ts$simplify(0:7)  # only keep samples with ids 0, 1, 2, 3, 4, 5, 6, 7
@@ -171,4 +171,8 @@ by `tskit`, and the one-based counting system used in `R`.
 
 ## Further information
 
-Be sure to check out the [reticulate](https://rstudio.github.io/reticulate/) documentation, in particular on [Calling Python from R](https://rstudio.github.io/reticulate/articles/calling_python.html), which includes important information on how R data types are converted to their equivalent Python types. 
+Be sure to check out the [reticulate](https://rstudio.github.io/reticulate/)
+documentation, in particular on
+[Calling Python from R](https://rstudio.github.io/reticulate/articles/calling_python.html),
+which includes important information on how R data types are converted to their
+equivalent Python types.