gimp: refresh (#7896)

* Add link to `krita`

* Sync format with `krita` page:
- fix descriptions
- fix placeholders

* Fix description syntax and remove ".ext"

* Simplify placeholders

pages/common/gimp.md

@@ -1,24 +1,25 @@
 # gimp
 
 > GNU image manipulation program.
+> See also: `krita`.
 > More information: <https://docs.gimp.org/en/gimp-fire-up.html#gimp-concepts-running-command-line>.
 
-- Launch GIMP:
+- Start GIMP:
 
 `gimp`
 
-- Launch GIMP without showing the splash screen:
+- Start without the splash screen:
 
 `gimp --no-splash`
 
-- Start a new GIMP instance, even if there is already a running one:
+- Open the specified files:
+
+`gimp {{path/to/image1 path/to/image2 ...}}`
+
+- Start the new instance, even if there is already a running one:
 
 `gimp --new-instance`
 
-- Open the given file as a new image:
-
-`gimp --as-new {{path/to/image}}`
-
 - Print errors and warnings to the console instead of showing them in a dialog box:
 
 `gimp --console-messages`