Add markdown template (#209)

source/templates/markdown/README.md

@@ -0,0 +1,29 @@
+### 📒 Markdown (🚧 v3.7)
+
+Markdown template can render a **markdown template** by interpreting **templating brackets** `{{` and `}}`.
+
+<table>
+  <td align="center">
+    <img width="900" height="1" alt="">
+  </td>
+</table>
+
+It can be used to render custom markdown which include data gathered by metrics.
+Unlike SVG templates, it is possible to include revelant hyperlinks since it'll be rendered as regular markdown.
+
+You can even mix it with SVG plugins for even more customization.
+
+See [example.md](/source/templates/markdown/example.md) for a markdown template example.
+
+#### ℹ️ Examples workflows
+
+```yaml
+- uses: lowlighter/metrics@latest
+  with:
+    # ... other options
+    template: markdown
+    filename: README.md      # Output file
+    markdown: TEMPLATE.md    # Template file
+    markdown_cache: .cache   # Cache folder
+    config_output: markdown  # Output as markdown file
+```