Added cfg to code example to botain RGI data (#882)
Added cfg to code example to botain RGI data (#882)

Without initialized cfg loading the get_rgi functions don't work:
`version = cfg.PARAMS['rgi_version']` throws `KeyError: 'rgi_version'`
bearecinos/oggm,anoukvlug/oggm,bearecinos/oggm,OGGM/oggm,juliaeis/oggm,TimoRoth/oggm,anoukvlug/oggm,OGGM/oggm,TimoRoth/oggm,juliaeis/oggm