Add achievements plugin (#182)

source/plugins/achievements/README.md

@@ -0,0 +1,29 @@
+### 🏆 Achievements
+
+The *achievements* plugin displays several highlights about what you achieved on GitHub.
+
+<table>
+  <td align="center">
+    <img src="https://github.com/lowlighter/lowlighter/blob/master/metrics.plugin.achievements.svg">
+    <img width="900" height="1" alt="">
+  </td>
+</table>
+
+Achievements are mostly related to features offered by GitHub, so by unlocking achivements ranks you'll be mastering GitHub in no time!
+
+A few achievements contains actual real ranking (based on [GitHub search](github.com/search) results)!
+
+#### ℹ️ Examples workflows
+
+[➡️ Available options for this plugin](metadata.yml)
+
+```yaml
+- uses: lowlighter/metrics@latest
+  with:
+    # ... other options
+    plugin_achievements: yes
+    plugin_achievements_threshold: B       # Display achievements with rank B or higher
+    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
+```