I would definitely say you need to add a build card. It also needs to be typed with good English so it is easy for people to read and understand. Adding a build card helps judges as it gives extra information (no one is going to know everything and they certainly weren't there when you built the model) and viewers get the opportunity to learn more about the model if they are interested in it.
Keep it brief, this may mean if you have done a lot to a model you'll just be mentioning the highlights (or, in other words, what makes the build different) as people don't want to read reams of information. Judges often don't have the time to read a lot anyway. Add a few photos, but once again, don't overdo it.
Entering competitions pushes you as a builder and I enjoy entering them. However, the same model will do well in one but not place in another (sometimes up against the same competition) and judges will have opinions so don't waste time getting frustrated when you do not place in the top 3 (or whatever you goal may be at a particular show). Be pleasantly suprised when you are successful - there are a lot of good builders around and judging shows is not an easy task.