Add rule about 1 pkg at a time

[maelle]

Fix #876

I'll also need to add the Portuguese translation.

[maelle]

@beatrizmilz would you have time to review the Portuguese translation?

@yabellini would you have time to review the Spanish translation?

Thanks both! And no hurry.

[beatrizmilz]

@beatrizmilz would you have time to review the Portuguese translation?

@yabellini would you have time to review the Spanish translation?

Thanks both! And no hurry.

@maelle Sorry for taking so long. I reviewed it, and there is no fix needed for Portuguese!

[maelle]

Thanks @beatrizmilz!

[maelle]

And thanks @maurolepore!