Updated datum directory for PROJ 6 in GIS install instructions.
@@ -156,10 +156,11 @@ First, download the PROJ source code and datum shifting files [#]_::
$ wget https://download.osgeo.org/proj/proj-datumgrid-X.Y.tar.gz
Next, untar the source code archive, and extract the datum shifting files in the
-``nad`` subdirectory. This must be done *prior* to configuration::
+``data`` subdirectory (use ``nad`` subdirectory for PROJ < 6.x). This must be
+done *prior* to configuration::
$ tar xzf proj-X.Y.Z.tar.gz
- $ cd proj-X.Y.Z/nad
+ $ cd proj-X.Y.Z/data
$ tar xzf ../../proj-datumgrid-X.Y.tar.gz
$ cd ..
