Add template for Linux ~/Desktop/ icon file (merge from devbr6)

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@38895 15284696-431f-4ddb-bdfa-cd5b030d7da7

gui/icons/grass.desktop

@@ -0,0 +1,9 @@
+[Desktop Entry]
+Type=Application
+Encoding=UTF-8
+Name=GRASS GIS
+Comment=
+Categories=Application;Education;Geography;
+Exec=grass7
+Icon=/usr/share/icons/grass-48x48.png
+Terminal=true