another chart tool

service/documentation.md

@@ -664,6 +664,7 @@ See also [this LWN article](https://lwn.net/Articles/822969/).
 
 [vale]: https://errata-ai.gitbook.io/vale/
 [nodejs markdownlint]: https://github.com/DavidAnson/markdownlint
+
 ### Charts
 
 We currently use [Graphviz](https://graphviz.org/) to draw charts, but have also used
@@ -671,3 +672,4 @@ We currently use [Graphviz](https://graphviz.org/) to draw charts, but have also
 
  * [Mermaid](https://mermaid-js.github.io/mermaid/#/) - builtin to GitLab and GitHub
  * [Knotend](https://www.scottantipa.com/why-knotend)
+ * [Flowchart](https://flowchart.fun/)