Add explanation of "The pipe operator requires a function call as RHS" error

This error happens when you leave a pipe operator at the end of the last line of a pipeline and the following line starts with an object name, e.g.:

mpg |>
  head() |>
  
an_object <- 1:3

This was the number 1 error in the Week 2 assessment in 2022–23.

Also add this error to the list of common errors at

Line 555 in a0d8ee6

```{r common-errors, message=FALSE, warning=FALSE}

And add this to the common reasons for losing marks in the Week 2 assessment brief on Moodle.

This will be better handled in Week 2, to avoid overloading Week 1.

Moving this to Week 3 in the errors tutorials