Document use of gnome-screenshot

Author: radarhere

docs/reference/ImageGrab.rst

@@ -15,7 +15,10 @@ or the clipboard to a PIL image memory.
     returned as an "RGBA" on macOS, or an "RGB" image otherwise.
     If the bounding box is omitted, the entire screen is copied.
 
-    .. versionadded:: 1.1.3 (Windows), 3.0.0 (macOS), 7.1.0 (Linux (X11))
+    On Linux, if ``xdisplay`` is ``None`` then ``gnome-screenshot`` will be used if it
+    is installed. To capture the default X11 display instead, pass ``xdisplay=""``.
+
+    .. versionadded:: 1.1.3 (Windows), 3.0.0 (macOS), 7.1.0 (Linux)
 
     :param bbox: What region to copy. Default is the entire screen.
                  Note that on Windows OS, the top-left point may be negative if ``all_screens=True`` is used.

docs/releasenotes/9.2.0.rst

@@ -76,7 +76,9 @@ TODO
 Other Changes
 =============
 
-TODO
-^^^^
+Using gnome-screenshot on Linux
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-TODO
+In :py:meth:`~PIL.ImageGrab.grab` on Linux, if ``xdisplay`` is ``None`` then
+``gnome-screenshot`` will be used to capture the display if it is installed. To capture
+the default X11 display instead, pass ``xdisplay=""``.