Better documentation regarding the use of a custom tab bar component

[svenlombaert]

Related to: https://github.com/react-navigation/react-navigation-tabs/issues/116

There is little to no documentation about using a custom component as the tab bar with createBottomTabNavigator.

Some documentation about the required props + an explanation of what they mean could be very helpful.

[brentvatne]

yeah this could be useful. one way this is documented currently is in the themes docs page, notice that we override the bottom tab bar to theme it: https://reactnavigation.org/docs/en/themes.html

[svenlombaert]

I mainly had problems with the extra ones I had to provide, getAccessibilityRole, getAccessibilityStates and getButtonComponent. Figured it out eventually by having a look at the source code. Also, it's a bit hidden in the themes maybe? I didn't find it, but that might have been just me.

[brentvatne]

i wouldn't say it's hidden, it's exactly where it needs to be for themes, but i agree we need to have some information on this perhaps in the api reference section