updated CONTRIBUTING.md for fontawsome use

Author: JSchraff

CONTRIBUTING.md

@@ -6,3 +6,11 @@ If you want to contribute please follow this guideline.
 
 For editing fxml files, use the "JavaFX Scene Builder" in version 8.5.0.  
 Layouting is generally done with fxml files.
+
+For fontawesome support add Libraries 
+`de.jensd:fontawsomefx-commons:8.15`
+`de.jensd:fontawsomefx-fontawsome:4.7.0-5`
+to the "JavaFX Scene Builder"
+
+Scene Builder may sometimes delete unicode Charakters when fxml file is changed.
+reset Glyph Name to reset uniocode Charakter.