Added short explanation of libraries

Author: SableRaf

.github/ISSUE_TEMPLATE/1_new-library.yaml

@@ -7,6 +7,8 @@ body:
       value: |
         Thank you for your new library contribution to Processing!
 
+        Libraries are add-ons that extend the functionality of the Processing language ([read more](https://github.com/processing/processing4/wiki/Library-Overview)).
+
         Please provide the necessary information below.
 
         If you need help creating a library, see the [Library Guidelines](https://github.com/processing/processing4/wiki/Library-Guidelines) or ask on the [Processing Forum](https://discourse.processing.org/).