I am creating a ggplot2 graph with model, data points and couple horizontal lines. I need to be able to put a legend on the bottom of the chart that states blue color line is for the model, red is the max, orange is the threshold etc.

I have this so far:

```
ggplot(df, aes(DATE, RELATIVE_PERCENT)) + 
       geom_point(colour="black", size=0.8) + 
       geom_smooth(method="loess", size=1, colour="blue", se=T) + 
       scale_x_datetime(breaks = "1 hours") + 
       theme_bw() + 
       geom_hline(aes(yintercept = 100), col="red", size=1.5) + 
       ylab("Relative CPU Utilization") + 
       xlab("Date") + 
       ggtitle("DB CPU Utilization") + 
       geom_hline(aes(yintercept = 70), col="orange", size=1.5)

```

here is my sample data frame

dput(df)

```
structure(list(DATE = structure(c(1365717060, 1365717090, 1365717120, 
1365717150, 1365717180, 1365717210, 1365717240, 1365717270, 1365717300, 
1365717330, 1365717360, 1365717390, 1365717420, 1365717450, 1365717480, 
1365717510, 1365717540, 1365717570, 1365717600, 1365717630), class = c("POSIXct", 
"POSIXt"), tzone = ""), RELATIVE_PERCENT = c(26, 26, 26, 26, 
26, 26, 25, 26, 26, 27, 25, 26, 26, 26, 26, 26, 26, 27, 27, 27
)), .Names = c("DATE", "RELATIVE_PERCENT"), class = "data.frame", row.names = 5740:5759)

```