No Introduction Necessary
It's been commented that BIND has no introduction, saying 'what is a roleplaying game?', and I don't think it needs one.
Of course, nobody's picking this thing up in a 90's game store, et c., but I feel we have a deeper problem. I think that no RPG - including D&D - really needs an explanation of 'how to do roleplaying' or whatever.
I started out with a confused kid, who mixed in actions with a computer game (most likely the original Baldur's Gate). It was a mess, but I could see how the game should have played, and immediately wanted the books. My father bought me a basic set, and some more splat-books every time I visited him. Soon after I had quite a pile.
I read all of them haphazardly, then deeply, then skimmed them again, looking for interesting ideas. I made my own world with a series of notebooks and random pieces of paper. I had my own map icons.
And none of it worked.
For all people say 'you need to document', and 'read the documentation', none of that works as a real introduction. Documentation and descriptions mostly work only as add-ons to tribal knowledge, and being a lone-player, without a group, I had no tribe.
Just to cement quite how remote I was - journey with me to a tiny little finger out the side of Scotland, to a little village, take a bus 16 miles out to a smaller village, walk down the road until the street lights and tarmac end, and keep walking for ten minutes through the darkness until you find a small side-route sloping down towards the sound of running water. Add a dash of autism and ugly medical problems, and you've basically got the picture.
Back to my non-working first map - it didn't work, because it had trees. Not tree-symbols, but individual trees. It was so zoomed in, that the action was individually placed creatures, and plot was nowhere to be seen. The books (A,D&D 2nd Ed.) had made a good attempt at explaining everything, but who could have explained 'do not map at a proportion of 1 yard = 1 inch'? Every part of the 'world' I had written had no in-game application, no fit for a real storytelling group or A,D&D campaign.
Fast-forward a few years, I got pre-written adventure books and started to understand what the whole thing was supposed to be about a little better, and ended up homeless in Glasgow, where I would clumsily pull the adventure modules and personal notes into a single campaign. The results remained weird.
I don't think I really got the wider picture until sometime later, as I began to join up with people who had been part of the wider RPG community.
The Unbroken Web
RPG history has developed orally. From the time Arneson and Gygax began, people at their gaming table joined, played, and some few attempted the art of the Dungeon Master, and gained players of their own. The cycle continued, and the books seem like more of a by-product than a necessary cause. At heart, RPG spread through an oral history, with each table forming a link in a massive web, which began at the first gaming table.
I don't think anyone can really fit 'what is a roleplaying game' into a book, never mind an introduction. People learn through action, and the books exist to reference or jog people's memories. RPGs are folk-tales, and we cannot properly describe them. You can only learn by doing.