[GRASS-git] [OSGeo/grass] eae8ab: Document r.external issues with r.null (#91)

[Ken Mankoff]

  Branch: refs/heads/releasebranch_7_8
  Home:   https://github.com/OSGeo/grass
  Commit: eae8ab6ec7a18998fec48725cbf2771a679e908e
      https://github.com/OSGeo/grass/commit/eae8ab6ec7a18998fec48725cbf2771a679e908e
  Author: Ken Mankoff <mankoff at gmail.com>
  Date:   2019-09-01 (Sun, 01 Sep 2019)

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

  Log Message:
  -----------
  Document r.external issues with r.null (#91)

* Add r.external issues with r.null