What to mention in your introduction to your research methodology chapter
Answer this question in less than one minute, assuming that I have the basic knowledge of your area:
What is your research about?

Than add these in less than two minutes:
Why did you do your research in that specific topic? What is your innovation?

Lastly,
How did you do it?

Now, write your answers on a paper. And that would be the intro.
Edit: Commentors are right. Only the last part would be an intro for methodology.