Add ability to build using docker

Signed-off-by: Knut Ahlers <knut@ahlers.me>

Makefile

@@ -2,7 +2,10 @@ TASMOTA_VERSION=v5.11.1
 
 default: build_sonoff build_sonoff-minimal
 
-ci: clean default
+chown:
+	chown -R $(UID) build
+
+ci: full-clean default
 
 build_%: download update_user-config venv
 	cd tasmota && ../venv/bin/platformio run -e $*
@@ -10,12 +13,15 @@ build_%: download update_user-config venv
 	cp tasmota/.pioenvs/$*/firmware.bin build/$*.bin
 
 clean:
-	rm -rf tasmota build venv
+	rm -rf tasmota venv
 
 download:
 	git clone https://github.com/arendst/Sonoff-Tasmota.git tasmota
 	cd tasmota && git reset --hard $(TASMOTA_VERSION)
 
+full-clean: clean
+	rm -rf build
+
 update_user-config: venv
 	./venv/bin/python update.py
 	cd tasmota && git --no-pager diff -w sonoff/user_config.h

README.md

@@ -0,0 +1,18 @@
+# Luzifer / tasmota-build
+
+Inside this repostitory there is a small build environment to automatically configure and build a [Sonoff-Tasmota](https://github.com/arendst/Sonoff-Tasmota) image.
+
+## Usage
+
+- Adjust `config.yml` to your needs
+  - `!undef` ensures the parameter is not defined
+  - `!def` ensures the parameter is defined
+  - `${VAR}` reads the contents of the parameter from the environment
+  - Any other string will be inserted into the config
+- Define a `env` file for everything you are reading from the environment (Format: `VAR=VALUE`, one per line)
+- Build the firmware
+    ```bash
+    # docker run --rm -ti --env-file=env -e UID=$(id -u) -v $(pwd):/src -w /src python:2.7 make default clean chown
+    ```
+
+Pay attention: When defining strings you need to wrap them in double quotes for the compiler to understand them as strings: `PARAM: '"mystring"'`. If you are defining numbers you will define them like this: `PARAM: '1'`. Constants are used like this: `PARAM: CONSTANT`.