add mention to the string extraction capabilities to the README.md

[d-silveira]

First of all great work with this plugin,
now, I'd like to ask you to improve the README.md with a mention and perhaps a screenshot of the string extraction capabilities, namely the ability to select multliple languages to extract to, because it isn't obvious, and it should be, because it's great

Thanks,
Regards

[noordawod]

Thanks @d-silveira.
Could you submit a pr for this?