docs(nix): fix typo umu= { -> umu = {

README.md

@@ -145,7 +145,7 @@ If there is any problem with the flake feel free to open a bug report and tag an
 If you want to add umu-launcher as a flake add this to your inputs in `flake.nix`
 ```nix
   inputs = {
-    umu= {
+    umu = {
       url = "github:Open-Wine-Components/umu-launcher?dir=packaging/nix";
       inputs.nixpkgs.follows = "nixpkgs";
     };