Hey Rysia. There are a few guides available that already show you how place rune icons into your guide. There are two ways.
Greater Quintessence of Desolation (use double square brackets) will yield a small icon with the name/picture that gives the description when you place your cursor over it.
Greater Quintessence of Desolation
["icon=Greater Quintessence of Desolation size=50"] (without the quotes) will yield the same thing, only you can adjust the size as needed.
Greater Quintessence of Desolation
Hope this answers your question.
Nice guide by the way. :)

Yep, As Of 6th August, i have added the Harassing section in the build to help you and other people out. =)

Interesting guide, but could you please explain how to harrass with the Double Up ability, I play lots of AD carries but never understood how to harrass well with MF's double up.