[docs] Customize and tools docs completed

docs/user/tools/docs.user.tools.assignment.md

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+---
+{
+	"_label": "Assignment"
+}
+---
+
+You can assign any transaction to any user by clicking on the “Assign” button on the right hand column and adding a user.
+
+#### Step 1: Click on the Assign To Button
+
+![Assigned To](img/assigned-to.png)
+
+
+
+#### Step 2: Add the User and other details
+
+
+![Assign User](img/assignment.png)
+
+
+This transaction will appear in the To-do list of the user in “My List” section. It will also appear 
+in the “Assigned by me” section of the user, who has assigned this activity.