add readme for scenario gen

docs/ScenarioGeneration.md

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+
+# Scenario Generation
+
+This document provides a brief overview of the scenario generation process and how to use it.
+
+Most of these steps are also automated in the `Makefile` in the root directory of the repository.
+
+## Prerequisites
+
+### Downloading Population data
+
+See package `org.matsim.prepare.download` for downloading population data from regionalstatistik.de for Brandenburg and [Kommunalatlas](https://instantatlas.statistik-berlin-brandenburg.de/instantatlas/interaktivekarten/kommunalatlas/atlas.html)
+
+The Makefile references the downloaded files in the svn directory. (https://svn.vsp.tu-berlin.de/repos/shared-svn/projects/matsim-germany/regionalstatistik/)
+Re-downloading is normally not necessary.
+
+
+### Install Make
+
+The process is automated using the `Makefile` in the root directory of the repository. This requires `make` to be installed on your system.
+
+
+## Running scenario generation
+
+The first step prepares the network and population plans needed for (counts) calibration:
+This step also prepares the commercial traffic and can take longer if it is not already prepared.
+
+```bash
+make prepare-calibration
+```
+
+TODO: Add more details on the calibration process
+
+
+```bash
+make prepare-initial
+```
+
+
+```bash
+make prepare
+```
+
+
+### Mode calibration
+