Command "git [command] --help" opens as HTML in my code editor - no output to terminal. How do I revert to default behavior?
This is not the default behavior of git so you have made some local config change to cause this to happen.  Look in your ~/.gitconfig to see if there's anything that doesn't make sense to you.  Try commenting it out.  The core.pager setting is one of the first things I would check.  This stackoverflow question has a variety of options for dealing with this sort of thing.
update 1
I haven't tried to get this sort of thing to work, but according to the docs you can also specify a man.viewer to define the program that is going to run.  Do you get any errors if you try git help -w reset?
One work around would be to get the help to show up in the terminal by using git help -m reset.  By using the help subcommand instead of subcommand --help you can specify whether you want it to try man, info, or web.