title: Add main title multiple plots ggarange
body: <p>I have one data frame <code>dt</code> with data about dive behavior and at three different areas <code>BA, MI, FA</code>.
  I want to add main title to my multiple plots (<code>ba, mi, fa</code>) using <code>ggarrange</code>, but I didn't find something that worked.
  I want to add main title &quot;Dive depths (m)&quot; at top of my 3 plots</p>
  <pre><code>library(data.table)
  library(ggplot2)
  
  dt = data.table(area= c(&quot;BA&quot;, &quot;FA&quot;, &quot;MI&quot;),
                  dmean = c(30, 50, 200, 76, 467, 87, 98, 10, 240, 176, 89, 400, 340, 10, 40, 54, 89, 340, 205),
                  sex = c(&quot;F&quot;, &quot;M&quot;))
  
  ba&lt;-ggplot(dt[dt$area==&quot;BA&quot;,], mapping = aes(y = dmean, x = sex, color = sex, fill=sex))+
    geom_violin(alpha=.5,scale = &quot;width&quot;,trim = FALSE, position=position_dodge(1))+
    ggtitle(&quot;Dive mean at BA and sex&quot;)+
    scale_y_log10(breaks = c(10, 30, 50, 100, 200, 300, 400, 500)) +   
    scale_fill_discrete(name=&quot;Social class&quot;,
                        labels=c(&quot;Female&quot;, &quot;Male&quot;))+
    xlab(&quot;Habitat&quot;)+
    ylab(&quot;Dive depth (m)&quot;)+
    theme_bw();ba
  
  mi&lt;-ggplot(dt[dt$area==&quot;MI&quot;,], mapping = aes(y = dmean, x = sex, color = sex, fill=sex))+
    geom_violin(alpha=.5,scale = &quot;width&quot;,trim = FALSE, position=position_dodge(1))+
    ggtitle(&quot;Dive mean at MI and sex&quot;)+
    scale_y_log10(breaks = c(10, 30, 50, 100, 200, 300, 400, 500)) +   
    scale_fill_discrete(name=&quot;Social class&quot;,
                        labels=c(&quot;Female&quot;, &quot;Male&quot;))+
    xlab(&quot;Habitat&quot;)+
    ylab(&quot;Dive depth (m)&quot;)+
    theme_bw();mi
  
  fa&lt;-ggplot(dt[dt$area==&quot;FA&quot;,], mapping = aes(y = dmean, x = sex, color = sex, fill=sex))+
    geom_violin(alpha=.5,scale = &quot;width&quot;,trim = FALSE, position=position_dodge(1))+
    ggtitle(&quot;Dive mean at FA and sex&quot;)+
    scale_y_log10(breaks = c(10, 30, 50, 100, 200, 300, 400, 500)) +   
    scale_fill_discrete(name=&quot;Social class&quot;,
                        labels=c(&quot;Female&quot;, &quot;Male&quot;))+
    xlab(&quot;Habitat&quot;)+
    ylab(&quot;Dive depth (m)&quot;)+
    theme_bw();fa
  
  t&lt;-ggarrange(ba, mi, fa, 
               ncol=3, nrow=1, common.legend = TRUE, legend=&quot;bottom&quot;);t
  
  #I tried insert:
   ggtitle = &quot;Dive depths (m)&quot;
   top = &quot;Dive depths (m)&quot;)
   top=textGrob(&quot;Dive depths (m)&quot;
  
  </code></pre>
  <p>Someone know how to do?</p>