r - How to add legend corresponding to geom_hline(yintercept = log(2000)) in ggplot2? -

i using geom_hline(yintercept = log(2000), linetype = "dotdash") in ggplot2 add horizontal line @ y = log(2000) in plot (attached below).

what want display legend "log(2000)" @ left side of y axis corresponding dash line. ideas?

the r code of plot given below:

library(ggplot2); library(scales)  set.seed(10) varx <- rep(c("group1", "group2"), each = 3) vary <- rep(c("a", "b", "c"), 2)     poi <- sample(20:30, 6) upper <- sample(40:50, 6) lower <- sample(1:10, 6)  dat <- data.frame(varx, vary, poi, upper, lower) dat #    varx vary poi upper lower #1 group1     25    43     2 #2 group1    b  23    42     6 #3 group1    c  29    45     3 #4 group2     30    50     4 #5 group2    b  20    44     1 #6 group2    c  21    47    10  pp <- ggplot(dat, aes(colour = varx, y = poi, x = vary))   limits <- aes(ymax = upper, ymin = lower)  pp  + geom_point(aes(shape=varx), position = position_dodge(0.3), size = 2) +    ## dodge make lines not stack upon each other   geom_errorbar(limits, size = 1, width = 0.15, position = position_dodge(0.3)) +    theme_bw() + ## rid of grey background   geom_hline(yintercept = log(2000), linetype = "dotdash") +   coord_cartesian(ylim = c(1, 60)) +    scale_shape_manual(values = c(17, 19)) +    theme(legend.justification= c(1, 0),          legend.position = c(1, 0.75),         legend.key = element_blank(),## rid of legend box          legend.title = element_blank(),         legend.text = element_text(size = 10, face = "bold"),         legend.background = element_rect(fill=alpha(0.0001))) +   labs(x = null, y = null) 

building on @lukea's comment

pp + scale_y_continuous(breaks = sort(c(log(2000), seq(0, 60, 10))),labels=c(0,"log(2000)",seq(10,60,10)))