remove unused whitespaces, add shell.nix and .envrc (#2749)

.envrc

@@ -0,0 +1 @@
+use_nix

README.md

@@ -451,6 +451,12 @@ pacman -S qt5-svg
 pacman -S openssl ca-certificates
 ```
 
+#### NixOS
+
+```shell
+nix-shell
+```
+
 #### MacOS
 
 First of all you need to install [brew](https://brew.sh) and than install dependencies

shell.nix

@@ -0,0 +1,11 @@
+{ pkgs ? import <nixpkgs> {} }:
+
+pkgs.mkShell {
+  nativeBuildInputs = with pkgs; [
+    cmake
+    qt5.full
+    qt5.qttools
+    qt5.qtsvg
+  ];
+  buildInputs = [ pkgs.qt5.qtbase ];
+}