Update 2.12.rst
Update 2.12.rst

Add details of 'add_sub_menus_inline' template tag option to release notes
ababic/wagtailmenus,ababic/wagtailmenus,rkhleics/wagtailmenus,rkhleics/wagtailmenus,ababic/wagtailmenus,rkhleics/wagtailmenus