added basic README

README.md

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+Provide a JSON REST API to `ESC/POS` printers. Most of the time these printers will be thermal printers. 
+
+# Usage
+
+GET `/api/printer/name` to get the UUID of the printer.
+
+GET `/api/printer/status` to get information about the current state of the printer.
+
+To actually print something use POST `/api/printer/print`. The body is an JSON array of print instructions. Following instructions are available.
+
+## Feed
+
+`lines` and `dots` can be used at the same time.
+
+```json
+{
+    "type":"feed",
+    "lines":4,
+    "dots":50
+}
+```
+
+## Text
+
+Only `text` is required.
+
+`alignment`: Can be `Right`,`Left`,`Center`. Default is `Left`.
+
+`underline`,`bold`,`doubleHeight`,`doubleWidth` are obvious and default to `false`.
+
+`fontB`: Use different font. Based on printer model. Default is `false`.
+
+`lineSpacing`: Line spacings in dots. Default is unset. 
+
+`newLine`: Insert a new line after printing the text. Default is `true`.
+
+```json
+{
+    "type":"text",
+    "text":"Hello world",
+    "alignment":"Center",
+    "underline": false,
+    "bold": false,
+    "doubleHeight":false,
+    "doubleWidth":false,
+    "fontB":false,
+    "lineSpacing":23,
+    "newLine":true
+}
+```
+
+## Barcode
+
+`barcode`: Value of the barcode. Depending on the `barcodeType` it may only contain numeric characters. Require.
+
+`barcodeType`: What type of barcode. Possible values are: `CODE128`, `UPC_A`,`UPC_E`,`JAN13_EAN13`,`JAN8_EAN8`,`CODE39`,`ITF`,`CODABAR_NW_7`,`CODE93`,`GS1_128`,`GS1_DATABAR_OMNIDIRECTIONAL`, `GS1_DATABAR_TRUNCATED`,`GS1_DATABAR_LIMITED`,`GS1_DATABAR_EXPANDED`. Default is `CODE128`. Depending on the printer modell not all types are supported.
+
+`barcodeCode`: I honestly have no idea what exactly this changes. But it changes something. Default is `CODE_B`.
+
+`alignment`: Just like `alignment` in the "Text" instruction. 
+
+`labelPos`: Position of the value of the barcode in text form. Possible values are : `None`, `Above`, `Below`, `Both`. Default is `Below`.
+
+`height`: Height of the barcode in dots. Default is unset.
+
+```json
+{
+    "type":"barcode",
+    "barcode":"348234445AA",
+    "barcodeType":"CODE128",
+    "barcodeCode":"CODE_B",
+    "alignment":"Center",
+    "labelPos":"None",
+    "height":45,
+}
+```