Let's get a more correct preface

Since people often start by reading the preface, let's get it a little bit more correct syntactically and grammatically speaking.
I'm not a native speaker either but I seem to have a bit more experience with English so let me serve as a first proof-reader (not very proof against mistakes but still...).

Note that I only corrected the first half for now (and there are still problems even in my corrections), I'll do the second half later.