chore: Add nix flakes support (#751)

README.md

@@ -452,6 +452,13 @@ pub enum Gender {
 }
 ```
 
+## Nix
+
+The prost project maintains flakes support for local development. Once you have
+nix and nix flakes setup you can just run `nix develop` to get a shell
+configured with the required dependencies to compile the whole project.
+
+
 ## FAQ
 
 1. **Could `prost` be implemented as a serializer for [Serde](https://serde.rs/)?**

flake.nix

@@ -0,0 +1,20 @@
+{
+  description = "Prost dependencies";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs { inherit system; };
+      in
+      {
+        devShells.default = pkgs.mkShell {
+          packages = with pkgs; [ cargo rustc ];
+          buildInputs = with pkgs; [ pkg-config protobuf curl ];
+        };
+      });
+}