That tells us what it means but for those of us that don't speak Japanese we still wouldn't know how to pronounce it.
My understanding is that the O is short - as in the English word "top". The U is a short "oo" as in the English word "flute" - not the same as "mute" which is longer and more like "you". The Japanese tend not to use long vowel sounds. R and K don't change much from their normal usage.
So basically it is "Rock-oo" but the oo is quite short and flows directly from the K with no break.
(Daughter is learning to speak, read and write Japanese at university, so if this is wrong, I shall blame her...)
Being someone who has studied a year of Japanese (and who has lived there for 2 months with a Japanese family and who has traveled there 4 or 5 times since), I can tell you that this is absolutely 100% incorrect.
The Japanse "alphabet" is comprised of somethng like 42 (might be more or less - it's been a while) sounds that are basically in English a consonant-vowel combination. The Japanese "vowels" are very similar to English. I'll use Roman lettering here for transliteration of the Japanese symbols:
a (pronounced like "ah")
i (pronounced like a long "e" - as in like key)
u (pronounced like "oo")
e (pronounced llike "ay")
o (pronounced like the Enlish long O).
Built off these are the rest of the sounds. The two we are interested in here are:
Ro is from the construction consisting of the letter "R" or the sound it makes (and it's actually a "rolled" R where the tip of the tounge touches the top gumline before making the sound - like you do when you sound the letter "L" - this is why Japanese have a hard time differentiating between the letters "R" and "L" because the sound is pretty much the same for them). So the grouping "Ro" comes from is:
So knowning how the vowel sounds are pronounced given above, "Ro" is basically pronounced like the English word Row except with the rolled R.
Ku comes from the grouping:
And so would be pronounced like "coo" (like the coo in coo-coo clock).
So the pronunciation is: