Add export description to Mermaid

README.md

@@ -207,6 +207,33 @@ digraph {
 This can then be rendered by tools that support the DOT graph language, such as the [dot command line tool](http://www.graphviz.org/doc/info/command.html) from [graphviz.org](http://www.graphviz.org) or [viz.js](https://github.com/mdaines/viz.js). See http://www.webgraphviz.com for instant gratification.
 Command line example: `dot -T pdf -o phoneCall.pdf phoneCall.dot` to generate a PDF file.
 
+### Export to mermaid graph
+
+It can be useful to visualize state machines on runtime. With this approach the code is the authoritative source and state diagrams are by-products which are always up to date.
+
+```csharp
+phoneCall.Configure(State.OffHook)
+    .PermitIf(Trigger.CallDialled, State.Ringing);
+
+string graph = MermaidGraph.Format(phoneCall.GetInfo());
+```
+
+The `MermaidGraph.Format()` method returns a string representation of the state machine in the [Mermaid](https://docs.github.com/en/get-started/writing-on-github/working-with-advanced-formatting/creating-diagrams#creating-mermaid-diagrams), e.g.:
+
+```
+stateDiagram-v2
+     [*] --> OffHook
+    OffHook --> Ringing : CallDialled
+```
+
+This can then be rendered by GitHub or [Obsidian](https://github.com/obsidianmd)
+
+``` mermaid
+stateDiagram-v2
+     [*] --> OffHook
+    OffHook --> Ringing : CallDialled
+```
+
 ### Async triggers
 
 On platforms that provide `Task<T>`, the `StateMachine` supports `async` entry/exit actions and so-on: