One of the things you will learn while progressing through today's job market is that the wider variety of career skills you have, the better chance you will have in getting work. This is particuarly true in the case of not for profit jobs, where you will often be required to wear multiple "hats." So while you might think that what you studied in college gives you all the skills you need for the kind of work you want, it not always enough.
If you have even just a basic knowledge of HTML, you will be even more attractive to not for profits. Yes, it may not be what you studied in school for 4+ years, but you have to do everything you can these days to get a leg up in a compeitive job market. Of course, this isn't the only career skill you can develop; I would recommend researching the kind of different skills that some of the top non profits are looking for, and consider taking continuing education courses in those subjects as well.