Add flake

flake.nix

@@ -0,0 +1,45 @@
+{
+  description = "stellar-cli development shell";
+
+  inputs = {
+    nixpkgs.url      = "github:NixOS/nixpkgs/nixos-unstable";
+    rust-overlay.url = "github:oxalica/rust-overlay";
+    flake-utils.url  = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, rust-overlay, flake-utils, ... }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        overlays = [ (import rust-overlay) ];
+        pkgs = import nixpkgs {
+          inherit system overlays;
+        };
+      in
+      with pkgs;
+      {
+        devShells.default = mkShell {
+          buildInputs = [
+            openssl
+            pkg-config
+            libudev-zero
+            jq
+            (rust-bin.stable.latest.default.override {
+              extensions = [ "rust-src" ];
+              targets = [ "wasm32-unknown-unknown" ];
+            })
+          ];
+          shellHook =
+          ''
+            echo `nix --version`
+            alias stellar="cargo run --bin stellar --"
+            SOROBAN_SECRET_KEY=SBPXU3OP65M2DQPRM4YFZ5NME66NWWH5DHN44IBDYAN4TFKKY7CS4OHY stellar keys add dev_key
+            export STELLAR_NETWORK=testnet
+            export STELLAR_ACCOUNT=dev_key
+            shell=$SHELL
+            shell=`basename $SHELL`
+            source <(stellar completion --shell $shell)
+          '';
+        };
+      }
+    );
+}