documentation to __object in execution run

docs/man/man7/cdist-type.text

@@ -252,6 +252,27 @@ echo "touch /etc/cdist-configured"
 --------------------------------------------------------------------------------
 
 
+VARIABLE ACCESS FROM THE GENERATED SCRIPTS
+------------------------------------------
+In the generated scripts, you have access to the following cdist variables
+
+- __object
+- __object_id
+
+but only for read operations, means there is no back copy of this
+files after the script execution.
+
+So when you generate a script with the following content, it will work:
+
+--------------------------------------------------------------------------------
+if [ -f "$__object/parameter/name" ]; then
+   name="$(cat "$__object/parameter/name")"
+else
+   name="$__object_id"
+fi
+--------------------------------------------------------------------------------
+
+
 HINTS FOR TYPEWRITERS
 ----------------------
 It must be assumed that the target is pretty dumb and thus does not have high