[GRASS-git] [OSGeo/grass] 487723: CONTRIBUTING.md: intro added for newcomers (#1566)

[Markus Neteler]

  Branch: refs/heads/master
  Home:   https://github.com/OSGeo/grass
  Commit: 487723b6aa1f2c3c49e9f4d2c2904c5b607fc0d6
      https://github.com/OSGeo/grass/commit/487723b6aa1f2c3c49e9f4d2c2904c5b607fc0d6
  Author: Markus Neteler <neteler at gmail.com>
  Date:   2021-05-08 (Sat, 08 May 2021)

  Changed paths:
    M CONTRIBUTING.md

  Log Message:
  -----------
  CONTRIBUTING.md: intro added for newcomers (#1566)

Related questions on grass-user suggested that there is a documentation gap. This PR attempts to fill it.