Merge pull request #7229 from RoziePlaysPython/imageopen_docs_fix

Update Image.show docs to list all viewers used on Linux

Author: radarhere

src/PIL/Image.py

@@ -2451,8 +2451,8 @@ def show(self, title=None):
         The image is first saved to a temporary file. By default, it will be in
         PNG format.
 
-        On Unix, the image is then opened using the **display**, **eog** or
-        **xv** utility, depending on which one can be found.
+        On Unix, the image is then opened using the **xdg-open**, **display**,
+        **gm**, **eog** or **xv** utility, depending on which one can be found.
 
         On macOS, the image is opened with the native Preview application.