update README.md for small-scale commercial traffic

contribs/small-scale-traffic-generation/README.md

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 # small scale traffic generation
 
-construction site; will contain small scale traffic generation code
+This provides a tool to generate small-scale commercial traffic. 
+
+The tool is based on :
+- IVV. Kleinräumige Wirtschaftsverkehrsmodelle. Endbericht zum Forschungsprojekt FE-Nr. 70.0689/2002/ im Auftrag des Bundesministeriums für Verkehr, Bau und Wohnungswesen. 2005. Download:
+[https://daten.clearingstelle-verkehr.de/194/](https://daten.clearingstelle-verkehr.de/194/).
+
+The description of the implementation in MATSim is given in the following paper :
+- R. Ewert and K. Nagel, “Agentenbasierte Modellierung des kleinräumigen Wirtschaftsverkehrs,” 2024. Accepted for publication at HEUREKA Conference 2024.
+
+## Model types
+The tool provides two different model types of small-scale commercial traffic. Therefore, you can select between the following options:
+- **commercialPersonTraffic**: This model contains the personal commercial traffic. This traffic has the objective to transport persons from one location to another. 
+- **goodsTraffic**: This model contains the goods traffic. This traffic has the objective to transport goods from one location to another.
+  - !! The long distance freight traffic is not included in this model. !! Therefore, see application contrib: [link](https://github.com/matsim-org/matsim-libs/tree/master/contribs/application/src/main/java/org/matsim/application/prepare/freight)  
+- **completeSmallScaleCommercialTraffic**: This model contains both, the personal commercial traffic and the goods traffic.
+
+
+## Input data
+- The generation model uses only open data.
+  - zone shape file:
+    - contains the zones for each region
+    - should contain columns: `areaID`, `region`
+  - structure data:
+    - *dataDistributionPerZone.csv*
+      - contains numbers of inhabitants and employees per sector for each `region`
+      - this file should be located next to the config file
+  - OSM data:
+    - Landuse
+      - should contain the following columns: `fclass`
+    - Buildings
+      - should contain the following columns: `type`, `levels`, `area`
+- Remarks:
+  - The zone shape file and the structure data should have the same regions.
+
+## Usage
+For generating the traffic, the following steps are necessary:
+- get necessary input data
+- run the tool by calling the main class `GenerateSmallScaleCommercialTrafficDemand`
+
+## Example
+An example is given as a test. See test `RunGenerateSmallScaleCommercialTrafficTest` and the mentioned example input data.
+