Update README and requirements.txt for face_landmark example (#57)

Author: davidzhao

examples/face_landmark/README.md

@@ -1,6 +1,9 @@
 ## FaceLandmark example
 
-Change the URL and TOKEN inside the script
+To run this demo:
 
-1. Download a model from https://developers.google.com/mediapipe/solutions/vision/face_landmarker#models
-2. Rename it to `face_landmarker.task` (as referenced by the code)
+1. pip install -r requirements.txt
+2. Download a model from https://developers.google.com/mediapipe/solutions/vision/face_landmarker#models
+3. Rename it to `face_landmarker.task` (as referenced by the code)
+4. Change the URL and TOKEN inside the script
+5. Connect to the same room from [another client](https://meet.livekit.io/?tab=custom)

examples/face_landmark/requirements.txt

@@ -0,0 +1,3 @@
+opencv-python
+mediapipe
+numpy