Achievements plugin: add option to change display style (#473)

source/plugins/achievements/README.md

@@ -5,6 +5,9 @@ The *achievements* plugin displays several highlights about what you achieved on
 <table>
   <td align="center">
     <img src="https://github.com/lowlighter/lowlighter/blob/master/metrics.plugin.achievements.svg">
+    <details><summary>Compact display</summary>
+      <img src="https://github.com/lowlighter/lowlighter/blob/master/metrics.plugin.achievements.compact.svg">
+    </details>
     <img width="900" height="1" alt="">
   </td>
 </table>
@@ -35,4 +38,5 @@ It also lets you quickly see at a glance what this user primarly use GitHub for,
     plugin_achievements_secrets: yes       # Display unlocked secrets achievements
     plugin_achievements_ignored: octonaut  # Hide octonaut achievement
     plugin_achievements_limit: 0           # Display all unlocked achievement matching threshold and secrets params
+    plugin_achievements_display: compact   # Use compact display
 ```