Add mime-type: toml

Hello!

Toml is a minimal configuration file format with the mime-type application/toml and the .toml file extension. Refer to https://toml.io/en/v1.0.0#mime-type

Currently, gio info outputs this on a toml file:

attributes:
  standard::icon: text-plain, text-x-generic, text-plain-symbolic, text-x-generic-symbolic

Spec (might be helpful)

• TOML is case-sensitive.
• A TOML file must be a valid UTF-8 encoded Unicode document.
• Whitespace means tab (0x09) or space (0x20).
• Newline means LF (0x0A) or CRLF (0x0D 0x0A).