Preview --live workflow & messages

[scharrier]

2 feedbacks after using the -- live option (which is really great, btw 👏 ).

• [x] When we launch the preview command with --live, we do not start by generating a preview. We directly get this message:

  Waiting for changes on file /Users/sebastien/Dev/bump/doc/api/v1/openapi.v3.yml...... ⣯
  

  I think that we should start by generating a preview, display the preview URL, and then. wait for changes in the file. As a user, I was expecting something like this:

  * Let's render a preview on Bump... done
  * Your preview is visible at: https://bump.sh/preview/fba0a2c0-cd1d-41c5-9c9d-ab77e52a9ce0 (Expires at 2021-11-11T18:25:11+01:00)
  Waiting for changes on file /Users/sebastien/Dev/bump/doc/api/v1/openapi.v3.yml... ⣯
  

• [ ] Also, it may be a good enhancement to display a message each time the file (and the preview) is updated, to inform the user that something is happening. I thought it wasn't working just because nothing new was written in my CLI.