Enhancements to the desktop entry (#6099)

- Add the argument %f to the Exec key so that a notebook file can be directly opened from the file manager by right-click → Open With Jupyter Notebook, or by double-clicking (https://specifications.freedesktop.org/desktop-entry-spec/latest/ar01s07.html)
- Add the Keyword key so that the Jupyter Notebook application can be searched with a keyword "python", e.g. from GNOME Shell (look for the Keywords key in the table https://specifications.freedesktop.org/desktop-entry-spec/latest/ar01s06.html)
- Add a semicolon ";" to the end of the strings in the Categories key (look at the examples here https://specifications.freedesktop.org/menu-spec/latest/ar01s03.html)

jupyter-notebook.desktop

@@ -1,10 +1,11 @@
 [Desktop Entry]
 Name=Jupyter Notebook
 Comment=Run Jupyter Notebook
-Exec=jupyter-notebook
+Exec=jupyter-notebook %f
 Terminal=true
 Type=Application
 Icon=notebook
 StartupNotify=true
 MimeType=application/x-ipynb+json;
-Categories=Development;Education
+Categories=Development;Education;
+Keywords=python;