[GRASS-git] [OSGeo/grass] a8aa37: r.horizon manual: explain negative values (#754)

[Markus Neteler]

  Branch: refs/heads/master
  Home:   https://github.com/OSGeo/grass
  Commit: a8aa37c9beb23db4c068b6d318b3a3ec30bdcded
      https://github.com/OSGeo/grass/commit/a8aa37c9beb23db4c068b6d318b3a3ec30bdcded
  Author: Markus Neteler <neteler at gmail.com>
  Date:   2020-07-02 (Thu, 02 Jul 2020)

  Changed paths:
    M raster/r.horizon/r.horizon.html

  Log Message:
  -----------
  r.horizon manual: explain negative values (#754)

- add explanations for the change in 688d5885557f22c7ea6618dcac3ddfbfc764731a
- related discussion:
    - https://lists.osgeo.org/pipermail/grass-user/2018-July/078870.html
    - cont'ed: https://lists.osgeo.org/pipermail/grass-user/2018-August/078887.html