Why do you need tabs in Markdown? I think they are just equivalent to space. If you want to use them in code blocks, no special syntax is required:
julia> """
`A\tA`
`A A`
"""
f()
f
help?> f
search: f fd for fma fld fld1 fill fdio frexp foldr foldl flush floor float first fill! fetch fldmod filter falses finally foreach fldmod1 findmin findmax findall filter! function Float64
A A
A A