allow scrolling in MD code

When I want to scroll a code example in MD in any readme to left or right, the app actually tries to switch e.g. from home area to notification area.

Expected:
When tapping first inside a code example in MD, hold the tap and move, then I'd expect that the actual embedded code preview is scrolled.

I'd like to tackle this issue myself as a first contribution, if you agree that this is an issue that needs to be fixed.

Start by reproducing the horizontal drag on a README code example, then trace the markdown rendering and touch handling that causes navigation to switch areas. Done means a tap-and-drag inside the embedded code preview scrolls it horizontally without triggering navigation.

Written by the indexing model from the issue text.