How to use heterogeneous parallelization with the taskset approach

[mandresm]

This answers the question of @khimstedt asked during the 02.08. Developer's meeting:

In order to activate Heterogeneous Parallelization using taskset one needs to add the following to the runscript:

computer:
    taskset: true # this one activates taskset approach when any model's omp_num_threads>1

<model>:
    omp_num_threads: <number_of_omp_threads> # This one is independent of the approach, it is used both for taskset and hetjobs approach

Please, @khimstedt let us know if you find any issues.