feat(plugins/sponsors): add new sponsors plugin (#548)

source/plugins/sponsors/README.md

@@ -0,0 +1,25 @@
+### 💕 GitHub Sponsors
+
+The *sponsors* plugin lets you display your sponsors and introduction text from [GitHub sponsors](https://github.com/sponsors/).
+
+<table>
+  <td align="center">
+    <img src="https://github.com/lowlighter/lowlighter/blob/master/metrics.plugin.sponsors.svg">
+    <details><summary>With GitHub sponsors introduction</summary>
+      <img src="https://github.com/lowlighter/lowlighter/blob/master/metrics.plugin.sponsors.full.svg">
+    </details>
+    <img width="900" height="1" alt="">
+  </td>
+</table>
+
+#### ℹ️ Examples workflows
+
+[➡️ Available options for this plugin](metadata.yml)
+
+```yaml
+- uses: lowlighter/metrics@latest
+  with:
+    # ... other options
+    plugin_sponsors: yes
+    plugin_sponsors_sections: goal, about # Display goal and about sections
+```