Enhance .env variable documentation

Hi,

Hope you're safe

Thanks so much for creating this 🤯

I've been trying to get this build running on multiple occasions over the past few weeks and I'm on the verge of giving up and using https://miniflux.app but I just wanted to try one last time tonight, hopefully with your help 🙏

> Copy .env.example to .env and fill ALL the variables - https://github.com/angristan/feedbin-docker#setup

Please make this file more descriptive e.g. variable options and/or comments?:

> FORCE_SSL=
> FORCE_SSL=[true | false | 'true' | 'false' | undefined]
> FORCE_SSL= // undefined == false

> Oh yeah that was one of the PR I made for Feedbin. If you're running as localhost without HTTPS, set FORCE_SSL=false, I forgot to add it (6d0a06d) - https://github.com/angristan/feedbin-docker/issues/1#issuecomment-585354566

NB seeing this in the same file confuses me:

> AWS_S3_PATH_STYLE="true"

If you have any issues (e.g. questions/queries) then happy to help

Keep up kind work!

Hope to hear back

Sincerely