lectures: add empty tex for demo lecture

.gitignore

 public/
+
+# Ignore latex files
+*.log
+*.aux
+*.bbl
+*.out
+*.blg
+*.toc
+*.nav
+*.snm
+*.dvi
+*.fls
+*_latexmk
+
+# Ignore ppt*, doc*, pdf
+*.ppt*
+*.pdf
+*.doc*

lectures_beamer/error_propagation.tex

+% !TEX program = xelatex
+
+\documentclass[aspectratio=169,20pt, USenglish]{beamer}
+
+\usetheme{ost}
+
+\graphicspath{{../static/img/}}
+
+\title{Error progragation}
+\subtitle{OST — Ostschweizer Fachhochschule}
+\date{\today}
+\author{JuanPi Carbajal}
+\institute{Institute for Energy Technology}
+
+\begin{document}
+
+\begin{frame}
+    \titlepage
+\end{frame}
+
+
+\end{document}