Fix #2872: update rng doc about thread/fork-safety
Fix #2872: update rng doc about thread/fork-safety

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