* add "info" command to CLI

As a convenience, add the info directive to CLI. Running `python transformers-cli info` will return a string containing the transformers version, platform, python version, PT/TF version and GPU support

* Swap f-strings for .format

Still supporting 3.5 so can't use f-strings (sad face)

* Add reference in issue to CLI

* Add the expected fields to issue template

This way, people can still add the information manually if they want. (Though I fear they'll just ignore it.)

* Remove heading from output

* black-ify

* order of imports

Should ensure isort test passes

* use is_X_available over import..pass

* style

* fix copy-paste bug

* Rename command info -> env

Also adds the command to CONTRIBUTING.md in "Did you find a bug" section