Start build when Codespace starts

.devcontainer/devcontainer.json

@@ -1,3 +1,9 @@
 {
-  "build": { "dockerfile": "Dockerfile" },
+  "build": {
+    "dockerfile": "Dockerfile"
+  },
+  "containerEnv": {
+    "PATH": "/opt/gcc/gcc-arm-10.3-2021.07-x86_64-aarch64-none-elf/bin:/opt/gcc/gcc-arm-10.3-2021.07-x86_64-arm-none-eabi/bin:${PATH}"
+  },
+  "postCreateCommand": "export RPI=3 && ./build.sh"
 }