update Gtk docs

README.md

@@ -114,9 +114,13 @@ on *Windows*, *Mac OS X* and other Unix-based operating systems as well.
 As shown in screenshots, there are multiple User Interface types (multiple
 ways to use the program).
 
-- **Gtk3-based interface**, uses [PyGI (Python Gobject Introspection)](http://pygobject.readthedocs.io/en/latest/getting_started.html)
+- **Gtk3-based interface**, uses [PyGI](http://pygobject.readthedocs.io/en/latest/getting_started.html)+Gtk3.
   See [doc/gtk3.md](./doc/gtk3.md) for how to install it on Linux and Mac OS X.
 
+- **Gtk4-based interface**, uses [PyGI](http://pygobject.readthedocs.io/en/latest/getting_started.html)+Gtk4.
+  See [doc/gtk4.md](./doc/gtk4.md).
+  This is still not as complete as Gtk3 interface.
+
 - **Tkinter-based interface**, meant to be used in the lack of Gtk. Specially on
   Windows where Tkinter library is installed with Python itself.
   You can [install Tkinter](./doc/tkinter.md) on Linux or Mac OS X.

doc/gtk3.md

@@ -3,8 +3,5 @@
 - Debian/Ubuntu: `apt install python3-gi python3-gi-cairo gir1.2-gtk-3.0`
 - openSUSE: `zypper install python3-gobject gtk3`
 - Fedora: `dnf install pygobject3 python3-gobject gtk3`
-- ArchLinux:
-- `pacman -S python-gobject gtk3`
-- https://aur.archlinux.org/packages/pyglossary/
+- ArchLinux: `pacman -S python-gobject gtk3`
 - Mac OS X: `brew install pygobject3 gtk+3`
-- Nix / NixOS: `nix-shell -p pkgs.gobject-introspection python38Packages.pygobject3 python38Packages.pycairo`

doc/gtk4.md

@@ -0,0 +1,7 @@
+## Gtk4 interface requirements
+
+- Debian/Ubuntu: `apt install python3-gi python3-gi-cairo gir1.2-gtk-4.0`
+- openSUSE: `zypper install python3-gobject gtk4`
+- Fedora: `dnf install pygobject3 python3-gobject gtk4`
+- ArchLinux: `pacman -S python-gobject gtk4`
+- Mac OS X: `brew install pygobject3 gtk4`