Add OSG section.

content/osg/_index.md

...ent/osg/a_simple_example_of_submitting_an_htcondor_job.md

content/osg/characteristics_of_an_osg_friendly_job.md

content/osg/how_to_submit_an_osg_job_with_htcondor.md

content/osg/using_distributed_environment_modules_on_osg.md

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