ogrmerge.py: add page (#7903)

pages/common/ogrmerge.py.md

@@ -0,0 +1,16 @@
+# ogrmerge.py
+
+> Merge several vector datasets into a single one.
+> More information: <https://gdal.org/programs/ogrmerge.html>.
+
+- Create a GeoPackage with a layer for each input Shapefile:
+
+`ogrmerge.py -f {{GPKG}} -o {{path/to/output.gpkg}} {{path/to/input1.shp path/to/input2.shp ...}}`
+
+- Create a virtual datasource (VRT) with a layer for each input GeoJSON:
+
+`ogrmerge.py -f {{VRT}} -o {{path/to/output.vrt}} {{path/to/input1.geojson path/to/input2.geojson ...}}`
+
+- Concatenate two vector datasets and store source name of dataset in attribute 'source_name':
+
+`ogrmerge.py -single -f {{GeoJSON}} -o {{path/to/output.geojson}} -src_layer_field_name country {{source_name}} {{path/to/input1.shp path/to/input2.shp ...}}`