README should not steer new users to overriding submit script template

[mbmilligan]

The current example configuration code in the README steers new users in an unhelpful direction:

batchspawner/README.md

Lines 84 to 93 in f465967

	c.TorqueSpawner.batch_script = '''#!/bin/sh
	#PBS -q {queue}@{host}
	#PBS -l walltime={runtime}
	#PBS -l nodes=1:ppn={nprocs}
	#PBS -l mem={memory}
	#PBS -N jupyterhub-singleuser
	#PBS -v {keepvars}
	module load python3
	{cmd}
	'''

If copied, this sample overrides the template script provided with the class, losing features that are implemented with template logic. The sample code should be replaced with one that uses the provided configuration variables (req_* etc) in accordance with recommended practice.