first step with drone ci

.drone.yml

@@ -0,0 +1,16 @@
+kind: pipeline
+type: docker
+name: default
+
+steps:
+  - name: build
+    image: espressif/idf:release-v4.1
+    commands:
+      - if [ -f sdkconfig ]; then
+      -   rm sdkconfig
+      - fi
+      - idf.py reconfigure
+      - echo "BB-CI-$((1 + RANDOM % 999))" > bbid
+      - sed -i -e s/BARBACK_ID=\"Barback\"/BARBACK_ID=\"`cat bbid`\"/ sdkconfig
+      - idf.py reconfigure
+      - idf.py build