add custom intercept line to qc_plot

[alex-d13]

Hi, thanks for the great tool!

I have a small question: I am trimming my reads at a certain base position based on the sequence quality. Could you help me how I can add a vertical line into my unfiltered qc_plot to indicate where I am trimming? I tried this, but the plot does not show the line:

p<-qc_plot(qc_file,modules = "Per base sequence quality")
        p + geom_vline(xintercept = 240, color = "red")

Cheers, Alex