docs: Enhance index.md with feature descriptions and links for core applications

Author: Vadym-Kharchenko

docs/site/index.md

@@ -13,12 +13,12 @@ This CRM is based on the [Django Admin site](https://docs.djangoproject.com/en/d
 
 Django CRM offers a comprehensive CRM solution and consists of the following core applications:
 
-- __TASKS__
-- __CRM__
-- __ANALYTICS__
-- __MASS MAIL__
+- __TASKS__ ([CRM task management](https://djangocrm.github.io/info/features/tasks-app-features){target="_blank"}: management of tasks, projects, memos)
+- __CRM__ ([CRM Application](https://djangocrm.github.io/info/features/crm-app-features){target="_blank"}: management of leads, contacts, companies, deals, products, etc.)
+- __ANALYTICS__ ([CRM Analytics software](https://djangocrm.github.io/info/features/analytics-app-features){target="_blank"}: sales funnel and other seven reports)
+- __MASS MAIL__ ([CRM email marketing](https://djangocrm.github.io/info/features/mass-mail-app-features){target="_blank"}: free mass email sender)
 
-The TASKS application does not require CRM configuration and allows individual users or teams to work with the following objects:
+The CRM task management does not require configuration and allows individual users or teams to work with the following objects and objects associated with them:
 
 - [Tasks](tasks_section.md#tasks) -> Subtasks
 - Projects -> Tasks -> Subtasks
@@ -42,3 +42,5 @@ To use all the features of these applications, you need to set up __CRM software
 - if necessary:
     - with the service of receiving [currency](currencies.md) exchange rates
     - with VoIP telephony service 
+
+---