gis/qgis: Fix README.

Signed-off-by: Willy Sudiarto Raharjo <willysr@slackbuilds.org>

gis/qgis/README.Slackware

@@ -30,13 +30,14 @@ system. These are the following
  - gpsbabel: for the GPS plugin
  - grass: for the Grass plugin
  - pdal: for support to PDAL
+ - libdraco: for support to Draco plugin
  - gsl: for georeferencing support
  - fcgi: for the QGIS server functionality
 
 The build install as optional dependencies - autodetected - also
-hdf5 and netcdf. If it is installed, the support of PDAL can be
-disabled also by setting to "no" the environment variable 
-   PDAL=no ./qgis.SlackBuild
+hdf5 and netcdf. If they are installed, the support of PDAL and/or
+Draco can be disabled also by setting to "no" the environment variable
+   PDAL=no [DRACO=no] ./qgis.SlackBuild
  
 2. PYTHON BINDINGS AND DEPENDENCIES
 The functionality of QGIS is strongly enhanced by a lot of plugins that
@@ -74,7 +75,7 @@ systems with old drivers/graphic cards. If you want to prevent this
 pass to the slackbuild the environment variable
 
    OPENCL=no ./qgis.SlackBuild
-   
+
 It has reported that QGIS shows runtime warnings about 'osgeo' unless
 the Python GDAL library is installed. If you encounter this issue you
 can solve by installing via pip the Python GDAL library as simple user