[manual] Mention the fact that editor instances are passed to lint functions

Closes #3113

doc/manual.html

@@ -2634,8 +2634,8 @@ editor.setOption("extraKeys", {
       to <code>true</code>, in which
       case <a href="#getHelper"><code>getHelper</code></a> with
       type <code>"lint"</code> is used to determined a validator
-      function. Such a function should, when given a document string
-      and an options object, return an array of <code>{message,
+      function. Such a function should, when given a document string,
+      an options object, and an editor instance, return an array of <code>{message,
       severity, from, to}</code> objects representing problems. When
       the function has an <code>async</code> property with a truthy
       value, it will be called with an additional second argument,