Add mindmap example to features

Signed-off-by: Yukai Huang <yukaihuangtw@gmail.com>

public/docs/features.md

@@ -380,6 +380,29 @@ stop
 -*O-o-
 ```
 
+### Mindmap
+
+```markmap
+# markmap-lib
+
+## Links
+
+- <https://markmap.js.org/>
+- [GitHub](https://github.com/gera2ld/markmap-lib)
+
+## Related
+
+- [coc-markmap](https://github.com/gera2ld/coc-markmap)
+- [gatsby-remark-markmap](https://github.com/gera2ld/gatsby-remark-markmap)
+
+## Features
+
+- links
+- **inline** ~~text~~ *styles*
+- multiline
+  text
+```
+
 > More information about **sequence diagrams** syntax [here](http://bramp.github.io/js-sequence-diagrams/).
 > More information about **flow charts** syntax [here](http://adrai.github.io/flowchart.js/).
 > More information about **graphviz** syntax [here](http://www.tonyballantyne.com/graphs.html)