Add MDX ArgTypes customization instructions

addons/docs/docs/props-tables.md

@@ -12,6 +12,7 @@ Storybook Docs automatically generates props tables for components in supported
 - [Controls](#controls)
 - [Customization](#customization)
   - [Customizing ArgTypes](#customizing-argtypes)
+  - [Custom ArgTypes in MDX](#custom-argtypes-in-mdx)
 - [Reporting a bug](#reporting-a-bug)
 - [Known limitations](#known-limitations)
 - [More resources](#more-resources)
@@ -196,6 +197,32 @@ Here are the possible customizations for the rest of the prop table:
 | `table.defaultValue.detail`  | A longer version of the default value (if it's a complex value)                                                           |
 | `control`                    | See [`addon-controls` README](https://github.com/storybookjs/storybook/blob/next/addons/controls/README.md#configuration) |
 
+### Custom ArgTypes in MDX
+
+To do the equivalent of the above customization [in MDX](./mdx.md), use the following.
+
+Overriding at the component level:
+
+```jsx
+<Meta
+  title="MyComponent"
+  component={MyComponent}
+  argTypes={{
+    label: { name: 'label' /* ... */ },
+  }}
+/>
+```
+
+And at the story level:
+
+```jsx
+<Story name="some story" argTypes={{
+  label: { name: 'label', ... }
+}}>
+  {/* story contents */}
+</Story>
+```
+
 ## Reporting a bug
 
 Extracting component properties from source is a tricky problem with thousands of corner cases. We've designed this package and its tests to accurately isolate problems, since the cause could either be in this package or (likely) one of the packages it depends on.