set up CI build

.github/workflows/rootfs.yml

@@ -0,0 +1,25 @@
+name: Build Root Filesystem
+
+on: [push, pull_request]
+
+jobs:   
+  rootfs:
+    runs-on: ubuntu-20.04
+    container:
+      image: nfriedly/buildroot-toolchain:master
+    steps:
+    - uses: actions/checkout@v2
+    - run: pwd
+    - run: echo $PATH
+    - name: build
+      run: |
+        #wget https://github.com/nfriedly/buildroot-toolchain/suites/5893824693/artifacts/200185195
+        #tar -xvf arm-buildroot-linux-musleabi_sdk-buildroot.tar.gz
+        #sudo mv arm-buildroot-linux-musleabi_sdk-buildroot /opt/miyoo
+        PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/opt/miyoo/bin:/opt/miyoo/arm-buildroot-linux-musleabi/sysroot/usr/bin
+make
+    - uses: actions/upload-artifact@v2
+      with:
+        name: rootfs.tar
+        path: output/images/rootfs.tar
+        if-no-files-found: error # 'error', 'warn', 'ignore'; defaults to `warn`