plotting docs: add :alt: text
plotting docs: add :alt: text

jpinedaf/pyspeckit,keflavich/pyspeckit,low-sky/pyspeckit,pyspeckit/pyspeckit,e-koch/pyspeckit,keflavich/pyspeckit,pyspeckit/pyspeckit,low-sky/pyspeckit,jpinedaf/pyspeckit,e-koch/pyspeckit