add wcs qgis, update wms qgis

documentation/user-guide/downloading.rst

documentation/user-guide/images/wcs_qgis1.png

documentation/user-guide/images/wcs_qgis2.png

documentation/user-guide/images/wcs_qgis3.png

documentation/user-guide/images/wms_qgis6.png

documentation/user-guide/viewing.rst