Create kernels directory

.github/workflows/build.yml

@@ -21,6 +21,8 @@ jobs:
       - uses: actions/checkout@v2
       - name: Get specific commits of git submodules
         run: sh -ex ./submod.sh
+      - name: Create kernels directory
+        run: mkdir -p kernels/
       - name: Put git hash in startup message
         run: |
           sed -i "s/Loading.../$(date +%Y%m%d)-$(git rev-parse --short HEAD)/g" src/userinterface.cpp