add 8.0 PDF (#945)

Author: jmckenna

en/download.txt

@@ -66,6 +66,7 @@ Current Release
 Previous Releases
 ..............................................................................
 
+* `MapServer-8.0-Documentation.pdf <https://download.osgeo.org/mapserver/docs/MapServer-80.pdf>`__ |image|
 * `MapServer-7.6-Documentation.pdf <https://download.osgeo.org/mapserver/docs/MapServer-76.pdf>`__ |image|
 * `MapServer-7.4-Documentation.pdf <https://download.osgeo.org/mapserver/docs/MapServer-74.pdf>`__ |image|
 * `MapServer-7.2-Documentation.pdf <https://download.osgeo.org/mapserver/docs/MapServer-72.pdf>`__ |image|