chore: capture Jenkins Docker baseline

installers/mcuxpresso/README.md

@@ -0,0 +1,27 @@
+# MCUXpresso installer
+
+Download "MCUXpresso Installer" (not a plain IDE package - NXP replaced that
+with an installer app) from https://www.nxp.com/mcuxpresso (NXP account
+required) and place the Linux download in this directory before running
+`docker compose build mcuxpresso-agent`.
+
+The file NXP ships is named something like `MCUXpressoInstaller.deb.bin` - a
+Makeself self-extracting archive wrapping an Electron app, not a `.deb` you
+can `apt install` directly. The Dockerfile unpacks it, pulls out the real
+`.deb` inside, and uses the app's bundled `MCUXpressoInstallerCLI` binary to
+fetch the toolchain non-interactively (no NXP login needed for the actual
+component downloads - see the Dockerfile for how). It picks up the first
+`*.deb.bin` it finds here, so you only need one file present at a time.
+
+By default the image bakes in the Arm GNU Toolchain, CMake, and Ninja (see
+`agents/mcuxpresso/Dockerfile`). To install additional packages/components
+(e.g. an MCUXpresso SDK bundle, LinkServer, SEGGER J-Link support), run:
+
+```bash
+docker run --rm jenkins-docker-mcuxpresso-agent mcux-cli install --help
+```
+
+to see every available `-p`/`-c` choice, then add them to the `mcux-cli
+install` line in the Dockerfile.
+
+This directory is gitignored except for this README.