Add gradio as a dependency?

[meg-huggingface]

Following the evaluate instructions, you eventually get to a point where you run app.py
When you run that, it mentions you need to check that gradio is installed -- but a bit hard to see because an error is immediately thrown (see below). Perhaps the instructions could specify to install gradio (pip install gradio), or else do it automatically, earlier, by including it with pip install evaluate[template] (if gradio is used for everything)?

(.env) bash-3.2$ python /Users/margaretmitchell/HuggingFace/git/data-measurements-tool/evaluate/npmi_debug/app.py
To create a metric widget with Gradio make sure gradio is installed.
Traceback (most recent call last):
File "/Users/margaretmitchell/HuggingFace/git/data-measurements-tool/evaluate/npmi_debug/app.py", line 6, in
launch_gradio_widget(module)
File "/Users/margaretmitchell/HuggingFace/git/data-measurements-tool/evaluate/src/evaluate/utils/gradio.py", line 97, in launch_gradio_widget
raise error
File "/Users/margaretmitchell/HuggingFace/git/data-measurements-tool/evaluate/src/evaluate/utils/gradio.py", line 94, in launch_gradio_widget
import gradio as gr
ModuleNotFoundError: No module named 'gradio'