title: read file and write text when find the line
body: <p>I have a file with many rows. I read it in line by line and finding a specific string, I need to insert another line after this.</p>
  
  <p>google          -Source file
  facebook</p>
  
  <p>google          -the file which should I get
  stasckoverflow
  facebook</p>
  
  <pre><code>using (var fs = File.Open(fileOutPath, FileMode.OpenOrCreate))
          {
                  using (StreamReader sr = new StreamReader(fs))
                  {
                      while ((line = sr.ReadLine()) != null)
                      {
                          if (line.StartsWith("google"))
                          {
  </code></pre>
  
  <p>what should I do to write "stasckoverflow" in the following line</p>