Added docs-nav parts

docs/en/tutorials/modular-crm/part-01.md

@@ -1,5 +1,15 @@
 # Creating the Initial Solution
 
+````json
+//[doc-nav]
+{
+  "Next": {
+    "Name": "Creating the initial products module",
+    "Path": "tutorials/modular-crm/part-02"
+  }
+}
+````
+
 Follow the [Get Stared](../../get-started/layered-web-application.md) guide to create a new layered web application with the following configuration:
 
 * **Solution name**: `ModularCrm`

docs/en/tutorials/modular-crm/part-02.md

@@ -1,5 +1,19 @@
 # Creating the Initial Products Module
 
+````json
+//[doc-nav]
+{
+  "Previous": {
+    "Name": "Creating the initial solution",
+    "Path": "tutorials/modular-crm/part-01"
+  },
+  "Next": {
+    "Name": "Building the products module",
+    "Path": "tutorials/modular-crm/part-03"
+  }
+}
+````
+
 In this part, you will build a new module for product management and install it to the main CRM application.
 
 ## Creating Solution Folders

docs/en/tutorials/modular-crm/part-03.md

@@ -1,3 +1,17 @@
 # Building the Products Module
 
-TODO
+````json
+//[doc-nav]
+{
+  "Previous": {
+    "Name": "Creating the initial products module",
+    "Path": "tutorials/modular-crm/part-02"
+  },
+  "Next": {
+    "Name": "TODO",
+    "Path": "tutorials/modular-crm/part-04"
+  }
+}
+````
+
+In this part, you will learn how to create entities, services and a basic user interface for the products module.