I learned the command line by using the command line. When I switched to Arch Linux, using bash was inevitable. It took many Google queries and reading many man pages to finally become comfortable in it.
What determined the outcome of your service was the convenience factor. To use it, the user needs to select the information, go to your webpage, and then submit it. It's too much work for the user.
OP's program removes 1/3rd of the steps, making it much easier for the user.
Yes, programming is taught inside of _some_ high schools. A shockingly low amount of high schools actually teach it though. Neither my high school nor other nearby high schools have any sort of computer science curriculum.
I'd recommend that OP have a solid portfolio and get a potential client interested, and then only reveal their age when entering into a contract or doing something where it matters.
A complete introduction to Git can be found at http://learn.github.com/p/intro.html. I know you mentioned that you're comfortable with Git, but some of the information there may be of some use.
GitHub has a series of help articles, which could be regarded as a manual of sorts. They're at https://help.github.com/
Well, of course you need to give the markdown extension to files which should be rendered as such. How else is Github supposed to know which files are markdown?
Github Pages is strictly for hosting static files. Thus, it's not meant for discussion between users. You're better of renting a VPS and hosting your project's website on it.
https://lh5.googleusercontent.com/--gAC0BE9NrA/UUCiUYUp90I/A...