gio: Add "D-Bus" and "DBus" to Cargo.toml keywords and description

One good way to keep Rust binary sizes down when using D-Bus is to use
`gio`’s D-Bus bindings and link dynamically to the system
`libgio-2.0.so`.

However, if you’re not already aware that `gio` provides D-Bus bindings,
it’s hard to discover that it does. For example, searching for "dbus" on
https://crates.io/ does not list `gio` as an alternative.

This commit addresses that by including the terms "D-Bus" and "DBus" in
the `gio` package keywords and description. We include both "D-Bus" and
"DBus" because that’s what other D-Bus crates, such as [`dbus`][1] and
[`zbus`][2], also do.

  ### Steps to reproduce
  1. Go to https://crates.io/search?q=dbus&sort=downloads

  ### Expected result
  `gio` is listed on the first page.

  ### Actual result
  `gio` is not listed at all, despite having enough total downloads to
  qualify for the top 10 results.

[1]: https://github.com/diwic/dbus-rs/blob/eee6bf5b2d9ff81fabd281cb24b222455f2b5919/dbus/Cargo.toml#L10C12-L10C28
[2]: https://github.com/z-galaxy/zbus/blob/3d3491dabe1914b619305e56e856b5c3555cca1b/zbus/Cargo.toml#L10C12-L10C36

Author: Martin Nordholts

gio/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "gio"
-keywords = ["glib", "gio", "gtk-rs", "gnome"]
+keywords = ["glib", "gio", "D-Bus", "DBus", "gtk-rs", "gnome"]
 readme = "README.md"
 documentation = "https://gtk-rs.org/gtk-rs-core/stable/latest/docs/gio/"
 description = "Rust bindings for the Gio library"