Add some stuff to the threading implementation documentation
Add some stuff to the threading implementation documentation

sklam/numba,stuartarchibald/numba,sklam/numba,gmarkall/numba,IntelLabs/numba,IntelLabs/numba,stonebig/numba,gmarkall/numba,numba/numba,stuartarchibald/numba,sklam/numba,seibert/numba,sklam/numba,stuartarchibald/numba,numba/numba,cpcloud/numba,numba/numba,cpcloud/numba,cpcloud/numba,stonebig/numba,seibert/numba,sklam/numba,stonebig/numba,gmarkall/numba,numba/numba,stuartarchibald/numba,gmarkall/numba,stonebig/numba,IntelLabs/numba,IntelLabs/numba,seibert/numba,numba/numba,seibert/numba,seibert/numba,cpcloud/numba,IntelLabs/numba,stuartarchibald/numba,cpcloud/numba,stonebig/numba,gmarkall/numba