Update add action pattern guidance (#11906)

Updated add action guidance to make icon usage clearer.

before | after
--|--
![Screenshot 2024-04-18 at 9 07
29 AM](https://github.com/Shopify/polaris/assets/8629173/152659ba-8680-4bd4-87bf-e926ceadb140)
| ![Screenshot 2024-04-18 at 9 07
00 AM](https://github.com/Shopify/polaris/assets/8629173/9382be14-3dcc-4234-8b98-c8a2e2e0564b)

Author: sarahill

.changeset/nervous-shoes-mate.md

@@ -0,0 +1,5 @@
+---
+'polaris.shopify.com': patch
+---
+
+Updated common action pattern add guiance

polaris.shopify.com/content/patterns/common-actions/variants/overview.mdx

@@ -30,15 +30,15 @@ url: /patterns/common-actions/overview
 
     ![Two tertiary buttons with the circle plus icon and an Add {object} label.](/images/patterns/common-actions/types/[email protected])
 
-    Use the circle plus icon in buttons that don’t have a defined container like tertiary buttons.
+    Default to the circle plus icon for add actions.
 
   </Medium>
 
   <Medium variant="do">
 
     ![Two secondary buttons with the plus icon and an Add {object} label.](/images/patterns/common-actions/types/[email protected])
 
-    Use the plus icon when a button has a defined shape or filled background. The plus icon supports the action while balancing the weight of the element with the rest of the UI.
+    Use the plus icon in `secondary` and `primary` [button](/components/actions/button?example=button-default) variants. The plus icon supports the action while balancing the weight of the filled shaped element with the rest of the UI.
 
   </Medium>
 
@@ -54,7 +54,7 @@ url: /patterns/common-actions/overview
 
     ![A select list of options with an add option at the botto of the list, outside of the scrollable area.](/images/patterns/common-actions/types/[email protected])
 
-    Place add actions at the bottom of a list of selectable options. For example, when picking a collection or tag to add to a product. Keep the action visible by placing it outside of the scrollable area.  
+    Place add actions at the bottom of a list of selectable options. For example, when picking a collection or tag to add to a product. Keep the action visible by placing it outside of the scrollable area.
 
   </Medium>
 
@@ -63,7 +63,7 @@ url: /patterns/common-actions/overview
     ![Two cards each with long lists of resources in a viewable state with a main add action in the list header.](/images/patterns/common-actions/types/[email protected])
 
     Place add actions in the header in long lists of resources.
-  
+
   </Medium>
 
   <Medium variant="do">