improve rule syntax documentation

DesignspaceEditor2.roboFontExt/html/index.html

@@ -693,8 +693,9 @@ <h3>Rules syntax</h3>
     # conditions that trigger the rule:
     # &lt;axis name&gt; startRange-endRange
     optical 500-1000
+    slant 15-30
 
-    # a condition set with two conditions
+    # multiple conditions in a single line, all conditions in condintion set must be TRUE to trigger the rule:
     weight 800-1000 width 200-1000
 
 # Please note: in these examples, lines starting with # are comments.