stm32f4: build: add docker-compose.yml

Pass /dev/bus/usb in order to be able to access the stlink interface
from within the Docker container.

Use GDB to work around stlink issue #532 [1].

[1] stlink-org/stlink#532

stm32/docker-compose.yml

@@ -0,0 +1,20 @@
+version: '3'
+services:
+  builder:
+    build: .
+    image: stm32:1.0
+    devices:
+      - /dev/bus/usb
+    volumes:
+      - ./demo:/tmp/build
+    command: >
+      sh -c 'cd /tmp/build/demo && \
+        make && \
+        (st-util --multi &) && \
+        cd /tmp/build/demo && \
+        arm-none-eabi-gdb \
+          -batch \
+          -ex "target extended-remote :4242" \
+          -ex "load" \
+          -ex "run" \
+          bin/outp.elf'