docs: reduced install efforts with creation of requirements.txt

requirements.txt

@@ -0,0 +1,3 @@
+sphinxcontrib-plantuml
+myst-parser
+sphinx_rtd_theme

sphinx/README.md

@@ -1,10 +1,5 @@
+# Installation
 
-## Installation ##
-
-```
-python3 -m venv venv
-source venv/bin/activate
-pip install sphinxcontrib-plantuml
-pip install myst-parser
-pip install sphinx_rtd_theme
-```
+1. Virtuelle Pythonumgebung erstellen: ```python3 -m venv venv```
+2. Virtuelle Umgebung aktivieren: ```source venv/bin/activate```
+3. Pakete aus ```requirements.txt``` installieren: ```pip install -r requirements.txt```