Add slurm plugin docs

[kaelynj]

Closes #3781

[abbycross]

Suggested change

	Instead, mid term, there can be two different modes that HPC users can specify:
	Instead, mid-term, there can be two different modes that HPC users can specify:

I'm not sure what mid-term refers to here (and once previously in this file) - does it mean "currently, but will probably change, because it's under development"?

[ohtanim]

@kaelynj I have finished to review with a couple of change requests. Could you please incorporate my comments ? Thanks,

[ohtanim]

"to control state, run tasks, and monitor"
would be
"to access, control, and monitor"

[ohtanim]

get_target should be changed to get_backend.

(Our git repo will be also changed soon)

[ohtanim]

This line should be changed to:
backend = get_backend(qrmi)

Our repo will also be updated soon.

[ohtanim]

target=target,
should be changed to:
backend=backend,

(Our repo will also be updated soon.)

[ohtanim]

This line should be changed to:

if job.done():
    pub_result = result[0]
    print(f"Counts for the 'meas' output register: {pub_result.data.meas.get_counts()}")
elif job.cancelled():
    print("Cancelled")
elif job.errored():
    print(qrmi.task_logs(job.job_id()))

(Our git repo will be updated soon)