docs: add documentation on customizing row selection

tests/dummy/app/components/examples/customizing-row-selection/template.hbs

@@ -0,0 +1,26 @@
+{{! BEGIN-SNIPPET docs-example-customizing-row-selection.hbs }}
+<EmberTable as |t|>
+  <t.head @columns={{this.columns}} />
+
+  <t.body
+    @rows={{this.rows}}
+    @onSelect={{action this.selectRows}}
+    @selection={{this.selection}}
+    as |b|
+  >
+    <b.row as |r|>
+      <r.cell>
+        <:select as |rowMeta onSelectionToggled|>
+          <YourCustomCheckboxComponent
+            @checked={{rowMeta.isGroupSelected}}
+            @onClick={{onSelectionToggled}}
+          />
+        </:select>
+        <:default as |value|>
+          {{value}}
+        </:default>
+      </r.cell>
+    </b.row>
+  </t.body>
+</EmberTable>
+{{! END-SNIPPET }}

tests/dummy/app/templates/docs/guides/body/row-selection.md

@@ -81,6 +81,14 @@ itself.
   {{demo.snippet label='component.js' name='docs-example-selection-modes.js'}}
 {{/docs-demo}}
 
+## Customizing Row Selection
+
+By default, Ember Table renders an input of type `checkbox` alongside an empty `span` element that can be styled to look like a checkbox. If you want to customize the checkbox however, you can pass a named block `:select` to the `EmberTd` component. This block will receive `rowMeta` and the `onSelectionToggled` action as yielded arguments:
+
+{{#docs-demo as |demo|}}
+  {{demo.snippet name='docs-example-customizing-row-selection.hbs'}}
+{{/docs-demo}}
+
 ## Aborting a Selection
 
 Row selection follows a <a href="https://embermap.com/topics/component-side-effects/data-down-actions-up">DDAU</a> pattern, whereby the `onSelect` action handler supplied to Ember Table has control over which rows become selected. To ignore a user selection, it suffices to simply do nothing in the action handler.
@@ -92,4 +100,4 @@ To reset all internal state relating to an attempted user selection, call the `a
 {{#docs-demo as |demo|}}
   {{demo.snippet name='docs-example-aborting-a-selection.hbs'}}
   {{demo.snippet label='component.js' name='docs-example-aborting-a-selection.js'}}
-{{/docs-demo}}
+{{/docs-demo}}