[groovyscripting] Described a way for code reuse (openhab#16361)

Signed-off-by: Oleg Andreych <kjiec4@gmail.com>

Author: OlegAndreych

bundles/org.openhab.automation.groovyscripting/README.md

@@ -21,6 +21,13 @@ log:set DEBUG org.openhab.core.automation
 
 For more information on the available APIs in scripts see the [JSR223 Scripting]({{base}}/configuration/jsr223.html) documentation.
 
+## Code reuse
+
+One can place *.groovy files with Groovy classes under `automation/groovy` configuration directory.  
+Those classes can be imported in JSR-223 scripts or the UI rules action with the usual Groovy `import` statement.
+
+To apply shared code changes, one has to restart the `openHAB Core :: Bundles :: Automation` bundle on the Console or an openHAB instance altogether.
+
 ## Script Examples
 
 Groovy scripts provide access to almost all the functionality in an openHAB runtime environment.