add gradio

throws an error if gradio isn't installed, suggest to add to requirements.txt

import gradio as gr
ModuleNotFoundError: No module named 'gradio'

requirements.txt

@@ -7,4 +7,5 @@ moviepy
 flow_vis
 imutils
 numpy
+gradio
 git+https://github.com/facebookresearch/co-tracker.git