Add link to snippets icon customisation from icons documentation

docs/advanced_topics/icons.md

@@ -10,6 +10,7 @@ Elements that use icons are:
 -   [Client-side components](extending_clientside_components)
 -   [Rich text editor toolbar buttons](extending_the_draftail_editor)
 -   [ModelAdmin menu](modeladmin_menu_icon)
+-   [Snippets](wagtailsnippets_icon)
 -   [StreamField blocks](custom_streamfield_blocks)
 
 This document describes how to choose, add and customise icons.

docs/topics/snippets/customising.md

@@ -69,6 +69,8 @@ class MemberViewSet(SnippetViewSet):
 register_snippet(MemberViewSet)
 ```
 
+(wagtailsnippets_icon)=
+
 ## Icon
 
 You can define an {attr}`~wagtail.snippets.views.snippets.SnippetViewSet.icon` attribute on the `SnippetViewSet` to specify the icon that is used across the admin for this snippet type. The `icon` needs to be [registered in the Wagtail icon library](../../advanced_topics/icons). If `icon` is not set, the default `"snippet"` icon is used.