github: add workflow to verify nix-shell

Signed-off-by: Harsh Shandilya <me@msfjarvis.dev>

.github/workflows/nix.yml

@@ -0,0 +1,31 @@
+on:
+  push:
+    branches:
+      - develop
+
+name: Verify nix-shell config
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v1
+
+    - uses: actions/cache@v2
+      with:
+        path: |
+          ~/.cargo/registry
+          ~/.cargo/git
+          target
+        key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
+
+    - name: Install Nix
+      uses: cachix/install-nix-action@v10
+      with:
+        nix_path: nixpkgs=channel:nixos-unstable
+
+    - name: Enter nix-shell
+      run: nix-shell --pure
+
+    - name: Run cargo check
+      run: cargo check