Use your latin (french) keyboard to get greek characters:

To get:αβγδε ζηθικλμ νξοπρσςτυφ χψωάὰα̑ω̑ smooth breathing
Type :abgde zê_tiklmnxop rrcsstufh_pô ôâvowel + q
 
To get:ΑΒΓΔΕ ΖΗΘΙΚΛΜΝΞΟΠΡ ΣΤΥΦΧΨΩ rough breathingaccentsiota subscript
Type :ABGDE ZÊ_TIKLMNXOP RSTUFH_PÔ vowel (or r) + cvowel+é,è,âvowel+ç