Add a Repository: line to DESCRIPTION files

[aappling-usgs]

Not sure how CRAN does this, but packages you download from CRAN come with a Repository: CRAN line in their DESCRIPTION file. This line is used by packrat to learn how to get a .tar.gz bundle from an installed package; therefore, it'd be handy for our docker-packrat projects if GRAN added this line as well (as Repository: USGS to be consistent with the repo naming scheme used at https://owi.usgs.gov/R/gran.html).

See USGS-VIZLAB/gage-conditions-docker#1 (comment) for a use case.

[wdwatkins]

Looks like CRAN actually adds an entire block:

39 NeedsCompilation: no
 40 Packaged: 2017-09-28 14:59:21 UTC; ldecicco
 41 Author: Robert Hirsch [aut],
 42   Laura DeCicco [aut, cre],
 43   David Lorenz [aut],
 44   Jordan Read [ctb],
 45   Jordan Walker [ctb],
 46   Lindsay Carr [ctb],
 47   David Watkins [aut]
 48 Maintainer: Laura DeCicco <ldecicco@usgs.gov>
 49 Repository: CRAN
 50 Date/Publication: 2017-09-28 16:30:59 UTC
 51 Built: R 3.5.0; ; 2018-04-24 10:55:35 UTC; unix   

☝️ from the CRAN dataRetrieval description

[aappling-usgs]

Thanks - yes, CRAN does add more. Fine with me if GRAN also adds the complete block. But the only line packrat needs appears to be that Repository line