title: how can i add points to geom_line plot in ggplot
body: <p>I have a df as below and i wanted to generate time-series plot using geom_line. Here is the summary of my data:</p>
  
  <pre><code>summary(data.t.m)
                sample    side        time    day         variable       value       
   HA2015_E10AF.bam:  1   E:69   1      :12   F:72   nc.counts:138   Min.   : 4.346  
   HA2015_E10BF.bam:  1   W:69   2      :12   S:66                   1st Qu.: 6.949  
   HA2015_E10CF.bam:  1          3      :12                          Median : 8.529  
   HA2015_E11AF.bam:  1          4      :12                          Mean   : 9.085  
   HA2015_E11AS.bam:  1          5      :12                          3rd Qu.:10.501  
   HA2015_E11BF.bam:  1          6      :12                          Max.   :23.047  
   (Other)         :132          (Other):66                                          
  </code></pre>
  
  <p>Here is the code for generating the line plot:</p>
  
  <pre><code>plt &lt;- ggplot(data.t.m, aes(time, value, group = side, colour = side))
  plt &lt;- plt + stat_summary(fun.y = "mean", geom="line", size = 2, position=position_dodge(0.95))  
  plt &lt;- plt + stat_summary(fun.data="calc.sem", geom="errorbar")
  </code></pre>
  
  <p>The plot that is generated is as below...</p>
  
  <p><img src="https://i.stack.imgur.com/q4Y5q.png" alt="time_series_plot"></p>
  
  <p>Now my question is how can i add points corresponding to each of the time points on the ggplot?</p>