cli synonyms for --get-venv-dir and --check-updates

[r-ushil]

A quick change to address the following issues:

• Suggestion: Use -U as short option for --check-updates #418 : added -U as a synonym for --check-updates and updated man page
• Add --where option, as synonym for --get-venv-dir #409 : added --where as a synonym for --get-venv-dir and updated man page

[facundobatista]

Hello, this is great, thanks!!!

A couple of minor changes, I need to ask you:

• please move to --where the recommendation in the help message for --rm (in main.py), as the former should be the recommended way
• similarly, improve the README.rst file (which is the docs file)
• also annotate -U and --where as options in that file
• add yourself to the AUTHORS file (in alphabetical order)

Thanks!!!

[r-ushil]

Thanks Facundo, I've pushed the suggested changes. Let me know if this looks good!

[facundobatista]

Wonderful, thanks!!