Add DISABLE_QEMU=true to .env in devcontainer README.md

Author: lex-ibm

.devcontainer/README.md

@@ -7,6 +7,7 @@ Create a `.env` on the root of the project with the following content:
 GH_TOKEN=your_github_token
 npm_config_arch=your_architecture # Options are: x64, arm64, arm, riscv64, loong64, ppc64, and s390x
 _VSCODE_ARCH=your_vsc_architecture # Options are: x64, arm64, armhf, riscv64, loong64, ppc64le, and s390x
+# DISABLE_QEMU=true # Uncomment this if you prefer not to use the QEMU step in postinstall.js
 # Any other environment variable you want the tasks to run with or that set the build environment to your desired output architecture
 ```