docs: Specify how to use the prop renderIndicator in material-top-tab (react-navigation#419)

Author: brunohkbx

docs/material-top-tab-navigator.md

@@ -44,6 +44,7 @@ The route configs object is a mapping from route name to a route config.
   * `iconStyle` - Style object for the tab icon.
   * `style` - Style object for the tab bar.
   * `allowFontScaling` - Whether label font should scale to respect Text Size accessibility settings, default is true.
+  * `renderIndicator` - Function which takes an object with the current route and returns a custom React Element to be used as a tab indicator.
 
 Example:
 

website/versioned_docs/version-2.x/material-top-tab-navigator.md

@@ -43,6 +43,7 @@ The route configs object is a mapping from route name to a route config.
   * `iconStyle` - Style object for the tab icon.
   * `style` - Style object for the tab bar.
   * `allowFontScaling` - Whether label font should scale to respect Text Size accessibility settings, default is true.
+  * `renderIndicator` - Function which takes an object with the current route and returns a custom React Element to be used as a tab indicator.
 
 Example:
 

website/versioned_docs/version-3.x/material-top-tab-navigator.md

@@ -45,6 +45,7 @@ The route configs object is a mapping from route name to a route config.
   * `iconStyle` - Style object for the tab icon.
   * `style` - Style object for the tab bar.
   * `allowFontScaling` - Whether label font should scale to respect Text Size accessibility settings, default is true.
+  * `renderIndicator` - Function which takes an object with the current route and returns a custom React Element to be used as a tab indicator.
 
 Example: