Update vignettes/datatable-joins.Rmd

Co-authored-by: Michael Chirico <[email protected]>

vignettes/datatable-joins.Rmd

@@ -588,9 +588,9 @@ i <- data.table(i_int = c(2, 4, 5), UPPER = LETTERS[1:3])
 x[i, on = .(x_int >= i_int)]
 ```
 Key Takeaways:
-- The name of the output column (x_int) comes from x, but the values come from i_int in i.
-- The last row contains NA because no rows in x match the last row in i (UPPER = "C").
-- Multiple rows in x are returned to match the first row in i with UPPER = "A".
+- The name of the output column (`x_int`) comes from `x`, but the values come from `i_int` in `i`.
+- The last row contains `NA` because no rows in `x` match the last row in `i` (`UPPER == "C"`).
+- Multiple rows in `x` are returned to match the first row in `i` with `UPPER == "A"`.
 
 If you want to keep the i_int column from i, you need to explicitly select it in the result: