marktext: init at v0.16.0-rc.2

This uses the .AppImage binary release, until we have a real source package
(see https://github.com/marktext/marktext/issues/1647).

I used the `notable` package as a template.

pkgs/applications/misc/marktext/default.nix

@@ -0,0 +1,35 @@
+{ appimageTools, fetchurl, lib }:
+
+let
+  pname = "marktext";
+  version = "v0.16.0-rc.2";
+in
+appimageTools.wrapType2 rec {
+  name = "${pname}-${version}-binary";
+
+  src = fetchurl {
+    url = "https://github.com/marktext/marktext/releases/download/${version}/marktext-x86_64.AppImage";
+    sha256 = "1w1mxa1j94zr36xhvlhzq8d77pi359vdxqb2j8mnz2bib9khxk9k";
+  };
+
+  profile = ''
+    export LC_ALL=C.UTF-8
+  '';
+
+  multiPkgs = null; # no 32bit needed
+  extraPkgs = p: (appimageTools.defaultFhsEnvArgs.multiPkgs p) ++ [
+    p.libsecret
+    p.xlibs.libxkbfile
+  ];
+
+  # Strip version from binary name.
+  extraInstallCommands = "mv $out/bin/${name} $out/bin/${pname}";
+
+  meta = with lib; {
+    description = "A simple and elegant markdown editor, available for Linux, macOS and Windows.";
+    homepage = "https://marktext.app";
+    license = licenses.mit;
+    maintainers = with maintainers; [ nh2 ];
+    platforms = [ "x86_64-linux" ];
+  };
+}

pkgs/top-level/all-packages.nix

@@ -4906,6 +4906,8 @@ in
 
   mandoc = callPackage ../tools/misc/mandoc { };
 
+  marktext = callPackage ../applications/misc/marktext { };
+
   mawk = callPackage ../tools/text/mawk { };
 
   mb2md = callPackage ../tools/text/mb2md { };