add nix build shell

README.md

@@ -28,6 +28,8 @@ You can download and run already built binaries from [releases](https://github.c
 You can build Alfis by issuing `cargo build` and `cargo run` commands in a directory of cloned repository.
 If you want to build release version you need to do `cargo build --release` as usual.
 
+If you have the Nix package manager on Linux/Mac/Windows, an initial `shell.nix` is provided that provides build tools and dependencies. Run `nix-shell` to enter it, then run `cargo build` and `cargo run` as listed above.
+
 ### ![Windows Logo](/img/windows.svg) On Windows
 You don't need any additional steps to build Alfis, just stick to the MSVC version of Rust.
 
@@ -56,6 +58,9 @@ Install from available [AUR package](https://aur.archlinux.org/packages/alfis) c
 yay -S alfis
 ```
 
+### On NixOS
+`nix-shell` in this repo and then run `cargo build` and `cargo install` after you have entered the shell
+
 ## Installation
 
 ### Debian/Ubuntu (only blockchain DNS, without GUI)
@@ -95,4 +100,4 @@ If you want it to load config from another file you can command it so: `alfis -c
 1. Stabilize blockchain functions (domain transfer, info & contacts in UI), bug hunting and fixing.
 2. Change DNS server/proxy to own resource saving implementation (using trust-dns-proto for RR parsing).
 3. P2P traffic encryption (ECDH).
-4. Web-GUI to manage you node from browser.
+4. Web-GUI to manage you node from browser.