add png option to readme

README.md

@@ -1,6 +1,8 @@
 # OpenProject Workflow Visualiser
 This script parses a downloaded HTML of the Administration>Workflow page in OpenProject and extracts the default workflow of the previously selected role and type as a Mermaid stateDiagram-v2. It's recommended to download the workflow page with the checkmark set for only showing states used by the type. 
 
+In case you have mermaid-cli installed on your system and mmdc in your '$PATH', you can use the '-o' option to output a PNG rendering of your diagram. This option won't output a markdown representation.
+
 ## Example (role: Project Manager, type: Epic)
 In this example the role is allowed to act on all states or the work package.