title: add xmlElement into a XmlNode
body: <p>How to add an element into a XmlNode.</p>
  
  <pre><code>var xmlDoc = new XmlDocument();
  xmlDoc.Load(AppDomain.CurrentDomain.SetupInformation.ConfigurationFile);
  XmlNode nodes = xmlDoc.SelectSingleNode("/configuration/schedulers");
  </code></pre>
  
  <p>XML Example:</p>
  
  <pre><code>&lt;schedulers&gt;
  &lt;Scheduler name="test1" alert="4" timerType="type1" cronExpression="0/10 * * * * ?"&gt;
    &lt;property name="customerName" value="customerA" /&gt;
  &lt;/Scheduler&gt;
  &lt;Scheduler name="test2" alert="3" timerType="type2" cronExpression="0/15 * * * * ?" /&gt;
  &lt;Scheduler name="test3" maxFailureAlert="3" timerType="Type3" cronExpression="0/20 * * * * ?" /&gt;
  </code></pre>
  
  <p></p>
  
  <p>And I want to add new scheduler</p>
  
  <pre><code>&lt;schedulers&gt;
    &lt;Scheduler name="test1" alert="4" timerType="type1" cronExpression="0/10 * * * * ?"&gt;
      &lt;property name="customerName" value="COMMON_MODEL" /&gt;
    &lt;/Scheduler&gt;
    &lt;Scheduler name="test2" alert="3" timerType="type2" cronExpression="0/15 * * * * ?" /&gt;
    &lt;Scheduler name="test3" maxFailureAlert="3" timerType="Type3" cronExpression="0/20 * * * * ?" /&gt;
    &lt;Scheduler name="test4" maxFailureAlert="3" timerType="Type3" cronExpression="0/50 * * * * ?" /&gt;
  &lt;/schedulers&gt;
  </code></pre>