I'm glad you are concerned about documentation. Poor quality docs are the bane of many opensource projects. The most important thing you can do is draft your initial docs and then have someone with the minimal level of expertise or experience try to install/implement your code using only the docs. The stumbling blocks that the user reports will tell you where your docs are lacking. Ideally, after you make the first adjustments to the docs, you should find someone else to test them on. Repeat this process with new people until you have good docs.

Also, include a good project summary. You'd be surprised how many projects don't include that. They just assume that everyone knows who they are and what their code does.

Also, please have an accurate changelog.