@Roy93
When guests book your place they receive two emails - a 'reservation confirmed' email and 'your receipt from airbnb' invoice email.
On the 'reservation confirmed' email, here appears a red box to click on called ' view full itinerary' - if the guest clicks on this box then further information appears and here it lists useful things like your house rules, things your guest must acknowledge and also your directions.
It's not always obvious to the guest to go further and select the ''view full itinerary'' as the 'reservation confirmed' email shows most of the basic information they need ; such as booking dates and even your listings full postal address. By the listings address there is a hyperlink to 'get directions' however it doesn't show your directions but brings up a link to google maps instead.
So, your guests will be receiving your carefully written directions but from my experience the majority of guests are most likely blissfully unaware of your instructions as they are buried away in the confirmation e-mail.
What you may consider doing to save time is to write a template message up with your directions, save this template within your guest messages page, then use the 'send saved message' function to send to guests prior to their expected arrival.