add basic build info to README.md

.build.yml

@@ -11,6 +11,29 @@ steps:
   commands:
   - git submodule update --init --recursive
 
+- name: patch
+  image: alpine/git
+  depends_on: [ submodules ]
+  commands:
+  - |-
+    sed -i 's/GNU bash, version (3\\\.\[1-9\]|4)/GNU bash, version (3.[1-9]|4|5)/g' modules/sdk/crosstool-NG/configure.ac
+
+  - mkdir -p modules/sdk/crosstool-NG/.build/tarballs
+  - wget https://github.com/libexpat/libexpat/releases/download/R_2_1_0/expat-2.1.0.tar.gz -O modules/sdk/crosstool-NG/.build/tarballs/expat-2.1.0.tar.gz
+
+- name: toolchain
+  image: debian:sid
+  depends_on: [ patch ]
+  commands:
+  - apt update
+  - apt install -y make bash gawk g++ gcc libc6-dev flex bison automake autoconf gperf texinfo wget git bzip2 help2man libtool libtool-bin unrar-free unzip ncurses-dev libexpat-dev python-dev python3
+  - cd modules/sdk
+  - export CT_EXPERIMENTAL=y
+  - export CT_ALLOW_BUILD_AS_ROOT=y
+  - export CT_ALLOW_BUILD_AS_ROOT_SURE=y
+  - make standalone=y -j$(nproc)
+  - wget -N https://raw.githubusercontent.com/espressif/esptool/master/esptool.py -O xtensa-lx106-elf/bin/esptool.py
+
 - name: firmware
   image: docker-repo.service.intern.lab.or.it:5000/fiatlux-build-env
   depends_on: [ submodules ]