Cache nim-waku binary

.github/workflows/ci.yml

@@ -14,6 +14,15 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v2
 
+      - name: Init submodules
+        run: git submodule update --init --recursive
+
+      - name: Cache nim-waku binary
+        uses: actions/cache@v2
+        with:
+          path: ./nim-waku/build/wakunode2
+          key: nim-waku-build-v1-${{ hashFiles('.gitmodules') }}
+
       - name: Install bufbuild
         uses: mu-io/setup-buf@v1beta
         with: