Document @argfile option.

Bug: 567676
Change-Id: I8b602cf1fb35598a8b8a53878ffbab02ab66ae87
Signed-off-by: Gunnar Wagenknecht <gunnar@wagenknecht.org>
diff --git a/bundles/org.eclipse.jdt.doc.user/tasks/tasks-executionArgs.htm b/bundles/org.eclipse.jdt.doc.user/tasks/tasks-executionArgs.htm
index 49b9e0c..d62132f 100644
--- a/bundles/org.eclipse.jdt.doc.user/tasks/tasks-executionArgs.htm
+++ b/bundles/org.eclipse.jdt.doc.user/tasks/tasks-executionArgs.htm
@@ -1,3 +1,4 @@
+
 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
     "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
 <html lang="en" xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
@@ -67,6 +68,11 @@
             when the checkbox is checked. This is selected by default for a launch configuration using Java 14 and above.
           </li>
           <li>
+            <strong>@argfile</strong>: When the list of application-specific and VM arguments become very long
+            this checkbox can be checked. All arguments will then be written into a file and the file is
+            passed to the VM as single argument. This is only supported for a launch configuration using Java 9 and above.
+          </li>
+          <li>
             <strong>Working Directory</strong>: The working directory used for
             the launched process. To change from using the default working
             directory, select <strong>Other</strong> and specify the workspace