title: how to add dashed horizontal line with label in ggplot
body: <p>I have plotted a line plot. I have added a horizontal line on the plot. How to take horizontal line red dashed?</p>
  
  <pre><code># Sample Data 
  
  library(tidyverse)
  Month= c("Jan","Feb","Mar","Apr","May","Jun")
  a = c(11,10,9,8,4,8)
  
  test= data_frame(Month,a) 
  test$cum_total &lt;- cumsum(test$a)
  
  test$Month &lt;- factor(test$Month, month.abb)
  
  # ggplot
  
  ggplot(data=test, aes(x=Month, y=cum_total, group=1)) +
    geom_line()+
    geom_point()+
    geom_hline(yintercept=40)+
    annotate("text", x = "Feb", y = 40, label = "Previous Level", vjust = -0.5)
  </code></pre>