adds gnuplot and inkspace to installation requirements

docs/download/installation.md

@@ -16,6 +16,7 @@
 - [:simple-git: Git :octicons-link-external-16:](https://git-scm.com/downloads) *(must be accessible from a terminal, i.e. added to your PATH variable if not)*
 - [:fontawesome-brands-java: Java Runtime Environment :octicons-link-external-16:](https://jdk.java.net/) *(download zip file, unzip to e.g. `C:\Programs`, add `bin` folder of JDK to your **PATH** variable)*
 - [RCE :octicons-link-external-16:](https://rcenvironment.de/) *integration platform (download zip file, unzip to e.g. `C:\Programs`)*
+- [gnuplot :octicons-link-external-16:](https://sourceforge.net/projects/gnuplot/) for generating plots with matplot++
 
 !!! note
     Please check the [RCE Updates Website :octicons-link-external-16:](https://rcenvironment.de/pages/updatessecurity.html) for which Java version is working with the respective RCE version. Currently, e.g. Java **11.x** is recommended for the current released
@@ -24,6 +25,7 @@
 
 - [TiGL :octicons-link-external-16:](https://dlr-sc.github.io/tigl/) 3.x for visualizing the aircraft geometry
 - [MikTex :octicons-link-external-16:](https://miktex.org/) for creating pdf reports
+- [Inkscape :octicons-link-external-16:](https://inkscape.org/release/inkscape-1.4/) for creating plots for pdf reports
 
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