add x-twitter social icon

[boykush]

resolve issue #39

I have confirmed that the icon is displayed by adding the following code to config.toml in the forked version.

socials = [
  { name = "x-twitter", url = "https://twitter.com/boykush315", icon = "x-twitter" },
]

forked version page: https://boykush.github.io/

[not-matthias]

Thanks! :)