add usage info to readme

README.md

@@ -1,2 +1,23 @@
 # Mitgliederformulare
 
+## Latex im Dockercontainer
+
+- [Quelle](https://github.com/blang/latex-docker/)
+- Docker Image ändern in latexdockercmd.sh
+- derzeit das volle Ubuntu Image (~2.6GB)
+
+### Aufruf
+
+```bash
+mkdir -p build
+./latexdockercmd.sh pdflatex --output-directory=build <src>.tex
+mv build <src>.pdf .
+rm -r build
+```
+
+### Makefile
+
+```bash
+make
+make clean
+```