Display help information about git.

# To display help about a specific git subcommand:
git help <subcommand>

# To display help about a specific git subcommand in a web browser:
git help --web <subcommand>

# To display a list of all available git subcommands:
git help --all

# To list the available guides:
git help --guide

# To list all possible configuration variables:
git help --config