boards native_sim docs: Clarify which SDL version is needed

One needs the 32bit version of the SDL development library when
building for 32bit native_sim, and for the 64bit native_sim the
64bit version. Let's clarify this.

Also fix the SDL2 link.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>
1 file changed