Added docs into services

buisnesslogic/src/main/java/com/plannaplan/services/GroupService.java

@@ -9,6 +9,10 @@ import com.plannaplan.repositories.GroupRepository;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Service;
 
+/**
+ * Service of GroupService which can find(optional), get(By Course, Groups Ammount, Group By Id, find Not Existing Group), save, delete group.
+ */
+
 @Service
 public class GroupService {
     @Autowired