Document how to use tuples with numba.typed.List and numba.typed.Dict

[alanhdu]

Feature request

Right now, the docs for numba.typed.Dict say that:

Acceptable key/value types include but are not limited to: unicode strings, arrays, scalars, tuples.

But there are no examples of how to actually use it with tuples! I couldn't find how to construct a numba "tuple" class -- i had hoped that:

numba.typed.Dict.empty(
    key_type=(numba.types.unicode_type, numba.types.int32), 
    value_type=numba.types.float32, 
)

would work, but that fails at runtime (constructing the dictionary works fine, but actually inserting anything into it fails).

I ended up just using numba.typeof instead, but it'd be nice to have an example in the documentation!

(Thanks for this great feature BTW! This massively expands the places where I can use Numba!)

[stuartarchibald]

xref #3349 and #4497