docs: Mention GioUnix-2.0 GIR namespace alongside gio-unix-2.0.pc

This should clarify things a little for users of language bindings, who
don’t directly use `.pc` files.

Signed-off-by: Philip Withnall <pwithnall@gnome.org>

gio/gdesktopappinfo.c

@@ -70,7 +70,7 @@
  *
  * Note that `<gio/gdesktopappinfo.h>` belongs to the UNIX-specific
  * GIO interfaces, thus you have to use the `gio-unix-2.0.pc` pkg-config
- * file when using it.
+ * file or the `GioUnix-2.0` GIR namespace when using it.
  */
 
 #define DEFAULT_APPLICATIONS_GROUP  "Default Applications"

gio/gfiledescriptorbased.c

@@ -35,7 +35,7 @@
  *
  * Note that `<gio/gfiledescriptorbased.h>` belongs to the UNIX-specific
  * GIO interfaces, thus you have to use the `gio-unix-2.0.pc` pkg-config
- * file when using it.
+ * file or the `GioUnix-2.0` GIR namespace when using it.
  *
  * Since: 2.24
  **/

gio/gunixfdmessage.c

@@ -29,7 +29,7 @@
  *
  * Note that `<gio/gunixfdmessage.h>` belongs to the UNIX-specific GIO
  * interfaces, thus you have to use the `gio-unix-2.0.pc` pkg-config
- * file when using it.
+ * file or the `GioUnix-2.0` GIR namespace when using it.
  */
 
 #include "config.h"

gio/gunixinputstream.c

@@ -49,7 +49,7 @@
  *
  * Note that `<gio/gunixinputstream.h>` belongs to the UNIX-specific GIO
  * interfaces, thus you have to use the `gio-unix-2.0.pc` pkg-config
- * file when using it.
+ * file or the `GioUnix-2.0` GIR namespace when using it.
  */
 
 enum {

gio/gunixoutputstream.c

@@ -51,7 +51,7 @@
  *
  * Note that `<gio/gunixoutputstream.h>` belongs to the UNIX-specific GIO
  * interfaces, thus you have to use the `gio-unix-2.0.pc` pkg-config file
- * when using it.
+ * file or the `GioUnix-2.0` GIR namespace when using it.
  */
 
 enum {