That just means you have a local formula that knows how to build and install c, but you have not shared it with the community so no one else will have access to

That just means you have a local formula that knows how to build and install c, but you have not shared it with the community so no one else will have access to the formula. You'd need to fork, push to your fork, and create a pull request to the main homebrew repo to try for inclusion. Also, it is only my hunch that they wouldn't accept the formula--you can still try. I'd still rename the project to be more descriptive (dir-c?) as there are only two homebrew formulae that have single char names (R, which has been around since 1993 and Z, which I'm surprised got included).