[GRASS-git] [OSGeo/grass] 615e1c: r.volume manual: example and screenshot added (#903)

[Markus Neteler]

  Branch: refs/heads/releasebranch_7_8
  Home:   https://github.com/OSGeo/grass
  Commit: 615e1cfbebff5d426946819a30d93658b2e07d23
      https://github.com/OSGeo/grass/commit/615e1cfbebff5d426946819a30d93658b2e07d23
  Author: Markus Neteler <neteler at gmail.com>
  Date:   2020-08-20 (Thu, 20 Aug 2020)

  Changed paths:
    M raster/r.volume/r.volume.html
    A raster/r.volume/r_volume_lake.png

  Log Message:
  -----------
  r.volume manual: example and screenshot added (#903)

- water basin example added

Note: there is a discrepancy in the results of r.lake and r.volume!