Add translation notes

[dashaluna]

I'm going through the plugin adding translations. Some strings are very obscure, it would be great to add translator notes to the following:

I'm going to keep this issue open until I get to the end of all translations. I'll add comment when I'm finished and we can see if we need to split this issue into several.

Add notes for translators

• [ ] %s of %s https://github.com/humanmade/backupwordpress/blob/master/admin/schedule-form-excludes.php#L162
• [ ] Not clear that text refers to extensions https://github.com/humanmade/backupwordpress/blob/master/admin/extensions.php#L87
• [ ] Add articles on, at to internalization?
• [ ] Some words are not clear, i.e. Complete Hourly - the complete here could be interpreted as to finish hourly or as all of resources hourly https://github.com/humanmade/backupwordpress/blob/master/functions/interface.php#L296
• [ ] Should we use plural Files instead of File as people might get it literally, that's only one file is being backup? https://github.com/humanmade/backupwordpress/blob/master/functions/interface.php#L296

[pdewouters]

thanks @dashaluna !