1 in 10 people in the UK has dyslexia and to varying degrees. It has nothing to do with intelligence, but it can hold children back at school because it causes difficulties with reading and writing. It is something people are born with and cannot be cured, but there are tools that can be provided and techniques taught to make life easier. There is a lot of information on the internet (funnily enough not very much of it is particularly dyslexia friendly!) but this video on YouTube is a good start .
My school is working towards the formal award of Dyslexia Friendly School. Obviously a lot of it is to do with teaching methods and homework policies. But there is also a lot that can be done in the Library to make it more usable by pupils with dyslexia - and these changes need not cost the earth and can actually help all your users. They can also be applied in other library settings.
Make things easy to find:
You may have done an amazing induction to the Library at the beginning of the year, but you do need to have signs. The disorganisation aspect of dyslexia means that a pupil might need to be reminded of layout every time they come into the room. If a child struggles with reading then looking along the spines of books will be off-putting. Make sure you have pictures or symbols as well as Dewey Subject Headings on the top of the bays. Have a floor plan of the room which they can look at (or keep) showing the symbols. Hang a poster near the desk with pictures and descriptions of the locations of useful things (even if they have to ask you for everything) to help them know what you have - paper, scissors, dictionaries, reading rulers and overlays, all the usual stuff.