[ADD] studio: documentation about rainbow man (#711)

studio/use_cases.rst

@@ -8,4 +8,5 @@ Use Cases
    use_cases/models_fields
    use_cases/filters_status_bar
    use_cases/automated_actions
-   use_cases/views
+   use_cases/views
+   use_cases/rainbow_man

studio/use_cases/rainbow_man.rst

@@ -0,0 +1,23 @@
+===========================
+Customizing the Rainbow Man
+===========================
+
+The Rainbow Man in Odoo is an animation shown once the user completes certain tasks and clicks on
+certain buttons. It is a way to make the software fun to use, and rewarding, for employees.
+
+.. image:: media/rainbow/crm_rainbow.png
+   :align: center
+   :alt: View of a sales form and the tab properties and its rainbow man field in Odoo Studio
+
+| On most buttons in Odoo, such as *Send by Email*, *Confirm* or *Cancel*, once they are selected in
+  Studio, under their *Properties*, the *Rainbow Man* effect can be applied.
+| By default, the feature is active:
+
+- when opportunities are marked as won;
+- when users empty their inboxes;
+- when the user finishes a tour;
+- when the user finishes doing reconciliations.
+
+.. image:: media/rainbow/properties_rainbow.png
+   :align: center
+   :alt: View of a sales form and the tab properties and its rainbow man field in Odoo Studio