Added barcode documentation, fixed wrong barcode type

docs/Administration.md

@@ -0,0 +1,25 @@
+# Administration
+
+## Configuration
+### Environments
+(TODO: Explanation regarding appsettings.XYZ.json here)
+
+### Barcode type
+The barcode type can be set in the appsettings like this:
+```json
+{
+    //[...]
+    "BarcodeType": "code128",
+    //[...]
+}
+```
+The following barcodes are supported:
+- CODE128C
+- EAN13
+- EAN8
+- UPC
+- ITF14
+- ITF
+
+Make sure to type in the barcode format in lowercase.
+